Lymphocytosis

WBCs develop from stem cells in the bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types marrow and are called leukocytes Leukocytes White blood cells. These include granular leukocytes (basophils; eosinophils; and neutrophils) as well as non-granular leukocytes (lymphocytes and monocytes). White Myeloid Cells: Histology when circulating in the bloodstream. Lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology are 1 of the 5 subclasses of WBCs. Lymphocytosis is an increase in the number or proportion of the lymphocyte subclass of WBCs, often as a result of an immune response to infection (known as reactive lymphocytosis). Common presentations include fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy, and upper respiratory symptoms. Usually transient, lymphocytosis resolves on its own in most cases after resolution of the infection. In other situations, it may signal a lymphoproliferative disorder (known as clonal lymphocytosis). Diagnosis is based on peripheral blood smear Peripheral Blood Smear Anemia: Overview and Types, flow cytometry Flow cytometry Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake. X-linked Agammaglobulinemia, and potentially, a bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types marrow biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma. Management depends on the underlying cause.

Last updated: Sep 15, 2021

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Overview

Definition

Lymphocytosis refers to elevated levels of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology. This elevation most often results from increased production.

  • Lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology:
    • Agranulocytic WBCs 
    • Circulating immunocompetent cells that can recognize antigens in the blood 
    • Leave the bloodstream through lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy, then can reenter the blood
    • Vary in size from small (6–8 µm) to large (18 µm)
    • Lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology are 1 of the 5 subclasses of WBCs:
      • Neutrophils Neutrophils Granular leukocytes having a nucleus with three to five lobes connected by slender threads of chromatin, and cytoplasm containing fine inconspicuous granules and stainable by neutral dyes. Innate Immunity: Phagocytes and Antigen Presentation (approximately 56%)
      • Lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology (approximately 34%)
      • Monocytes Monocytes Large, phagocytic mononuclear leukocytes produced in the vertebrate bone marrow and released into the blood; contain a large, oval or somewhat indented nucleus surrounded by voluminous cytoplasm and numerous organelles. Innate Immunity: Phagocytes and Antigen Presentation (approximately 4%)
      • Eosinophils Eosinophils Granular leukocytes with a nucleus that usually has two lobes connected by a slender thread of chromatin, and cytoplasm containing coarse, round granules that are uniform in size and stainable by eosin. Innate Immunity: Phagocytes and Antigen Presentation (approximately 3%)
      • Basophils Basophils Granular leukocytes characterized by a relatively pale-staining, lobate nucleus and cytoplasm containing coarse dark-staining granules of variable size and stainable by basic dyes. Innate Immunity: Phagocytes and Antigen Presentation (approximately 0.3%)
  • Lymphocytosis corresponds to an absolute lymphocyte count (ALC):
    • > 4000 lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology/µL for adults 
    • > 8000 lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology/µL for children < 12 years
    • Equation: ALC = WBC (cells/µL) × (% lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology ÷ 100)
    • ALC is used to quantitate lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology in peripheral blood (rather than the percentage of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology in the WBC differential count).
    • Normal values for ALC may vary in different laboratories.
  • Of note: The term leukocytosis Leukocytosis A transient increase in the number of leukocytes in a body fluid. West Nile Virus refers to elevated levels of WBCs in general.

Lymphocyte subsets

  • T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions:
    • Represent 60%–80% of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology 
    • Responsible for cell-mediated immunity Cell-mediated immunity Manifestations of the immune response which are mediated by antigen-sensitized T-lymphocytes via lymphokines or direct cytotoxicity. This takes place in the absence of circulating antibody or where antibody plays a subordinate role. Squamous Cell Carcinoma (SCC), which focuses on the active destruction of infected or cancerous cells
    • Types of T lymphocytes T lymphocytes Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions:
      • Cytotoxic Cytotoxic Parvovirus B19 T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions: bind BIND Hyperbilirubinemia of the Newborn directly to cells containing antigens and destroy them
      • Helper T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions (CD4+): stimulate the production of antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions by B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions and produce substances that activate other T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions
      • Suppressor T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions (CD8+): suppress the response of B and T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions to antigens
  • B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions:
    • 10%–20% of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology
    • Responsible for humoral immunity (antibody production)
      • Focus Focus Area of enhancement measuring < 5 mm in diameter Imaging of the Breast on identifying antigens prior to cell infection 
      • Create antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions to antigens
  • Natural killer (NK) cells:
  • Memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment cells:
    • B or T lymphocytes T lymphocytes Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions that recognize previously encountered antigens
    • Direct an immune response more quickly on subsequent exposures  
    • Stored in lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy and spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen: Anatomy
    • Can provide lifelong immunity against certain pathogens (e.g., measles Measles Measles (also known as rubeola) is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae. It is highly contagious and spreads by respiratory droplets or direct-contact transmission from an infected person. Typically a disease of childhood, measles classically starts with cough, coryza, and conjunctivitis, followed by a maculopapular rash. Measles Virus and mumps Mumps Mumps is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae. Mumps is typically a disease of childhood, which manifests initially with fever, muscle pain, headache, poor appetite, and a general feeling of malaise, and is classically followed by parotitis. Mumps Virus/Mumps)

Epidemiology

  • Lymphocytosis is most commonly seen between ages 15 and 45.
  • Most often is due to a viral infectious Infectious Febrile Infant process

Etiology and Pathophysiology

Lymphocytosis may result from an increased production of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology (most common) or several additional mechanisms.

Increased production of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology

The production of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology may be increased because of:

  • Response to an infectious Infectious Febrile Infant process:
    • Viral (most common)
    • Bacterial 
    • Parasitic
  • Lymphoproliferative disorders:
    • Monoclonal B-cell lymphocytosis Monoclonal B-Cell Lymphocytosis Chronic Lymphocytic Leukemia (MBL)
    • CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia
    • Large granular lymphocytic (LGL) leukemia
    • Non-Hodgkin lymphoma Lymphoma A general term for various neoplastic diseases of the lymphoid tissue. Imaging of the Mediastinum
    • ALL
    • Persistent polyclonal B-cell lymphocytosis
  • Drug hypersensitivity Drug hypersensitivity Immunologically mediated adverse reactions to medicinal substances used legally or illegally. Type IV Hypersensitivity Reaction reactions, most commonly to:
    • Phenytoin Phenytoin An anticonvulsant that is used to treat a wide variety of seizures. The mechanism of therapeutic action is not clear, although several cellular actions have been described including effects on ion channels, active transport, and general membrane stabilization. Phenytoin has been proposed for several other therapeutic uses, but its use has been limited by its many adverse effects and interactions with other drugs. First-Generation Anticonvulsant Drugs
    • Allopurinol Allopurinol A xanthine oxidase inhibitor that decreases uric acid production. It also acts as an antimetabolite on some simpler organisms. Gout Drugs
    • Carbamazepine Carbamazepine A dibenzazepine that acts as a sodium channel blocker. It is used as an anticonvulsant for the treatment of grand mal and psychomotor or focal seizures. It may also be used in the management of bipolar disorder, and has analgesic properties. First-Generation Anticonvulsant Drugs
    • Vancomycin Vancomycin Antibacterial obtained from streptomyces orientalis. It is a glycopeptide related to ristocetin that inhibits bacterial cell wall assembly and is toxic to kidneys and the inner ear. Glycopeptides 
    • Sulfa drugs
  • Chronic inflammation Chronic Inflammation Inflammation, for example:
  • Other causes:
    • Hyperthyroidism Hyperthyroidism Hypersecretion of thyroid hormones from the thyroid gland. Elevated levels of thyroid hormones increase basal metabolic rate. Thyrotoxicosis and Hyperthyroidism
    • Severe medical stress:
      • Trauma
      • Cardiac Cardiac Total Anomalous Pulmonary Venous Return (TAPVR) emergencies
      • Status epilepticus Status Epilepticus A prolonged seizure or seizures repeated frequently enough to prevent recovery between episodes occurring over a period of 20-30 minutes. The most common subtype is generalized tonic-clonic status epilepticus, a potentially fatal condition associated with neuronal injury and respiratory and metabolic dysfunction. Nonconvulsive forms include petit mal status and complex partial status, which may manifest as behavioral disturbances. Simple partial status epilepticus consists of persistent motor, sensory, or autonomic seizures that do not impair cognition. Subclinical status epilepticus generally refers to seizures occurring in an unresponsive or comatose individual in the absence of overt signs of seizure activity. Seizures
Table: Infectious Infectious Febrile Infant processes associated with lymphocytosis
Type of infection Microbes/conditions
Viral
  • Members of herpesvirus family:
    • EBV EBV Epstein-barr virus (EBV) is a linear, double-stranded DNA virus belonging to the herpesviridae family. This highly prevalent virus is mostly transmitted through contact with oropharyngeal secretions from an infected individual. The virus can infect epithelial cells and B lymphocytes, where it can undergo lytic replication or latency. Epstein-Barr Virus
    • CMV
    • Varicella
    • Others
  • HIV HIV Anti-HIV Drugs, acute infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
  • Measles Measles Measles (also known as rubeola) is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae. It is highly contagious and spreads by respiratory droplets or direct-contact transmission from an infected person. Typically a disease of childhood, measles classically starts with cough, coryza, and conjunctivitis, followed by a maculopapular rash. Measles Virus
  • Mumps Mumps Mumps is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae. Mumps is typically a disease of childhood, which manifests initially with fever, muscle pain, headache, poor appetite, and a general feeling of malaise, and is classically followed by parotitis. Mumps Virus/Mumps
  • Rubella Rubella An acute infectious disease caused by the rubella virus. The virus enters the respiratory tract via airborne droplet and spreads to the lymphatic system. Rubella Virus
  • Influenza Influenza Influenza viruses are members of the Orthomyxoviridae family and the causative organisms of influenza, a highly contagious febrile respiratory disease. There are 3 primary influenza viruses (A, B, and C) and various subtypes, which are classified based on their virulent surface antigens, hemagglutinin (HA) and neuraminidase (NA). Influenza typically presents with a fever, myalgia, headache, and symptoms of an upper respiratory infection. Influenza Viruses/Influenza
  • Viral hepatitis
  • Adenovirus Adenovirus Adenovirus (member of the family Adenoviridae) is a nonenveloped, double-stranded DNA virus. Adenovirus is transmitted in a variety of ways, and it can have various presentations based on the site of entry. Presentation can include febrile pharyngitis, conjunctivitis, acute respiratory disease, atypical pneumonia, and gastroenteritis. Adenovirus
  • Coxsackie B virus Virus Viruses are infectious, obligate intracellular parasites composed of a nucleic acid core surrounded by a protein capsid. Viruses can be either naked (non-enveloped) or enveloped. The classification of viruses is complex and based on many factors, including type and structure of the nucleoid and capsid, the presence of an envelope, the replication cycle, and the host range. Virology
  • Enteroviruses, including poliovirus Poliovirus Poliomyelitis is an infectious disease caused by the poliovirus. This virus is a member of the Picornaviridae family. It is a small, single-stranded, positive-sense RNA virus without a lipid envelope. Transmission occurs through the fecal-oral route and, occasionally, through respiratory aerosols. Poliovirus/Poliomyelitis
Bacterial
  • Pertussis Pertussis Pertussis, or whooping cough, is a potentially life-threatening highly contagious bacterial infection of the respiratory tract caused by Bordetella pertussis. The disease has 3 clinical stages, the second and third of which are characterized by an intense paroxysmal cough, an inspiratory whoop, and post-tussive vomiting. Pertussis (Whooping Cough)
  • Tuberculosis Tuberculosis Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis complex bacteria. The bacteria usually attack the lungs but can also damage other parts of the body. Approximately 30% of people around the world are infected with this pathogen, with the majority harboring a latent infection. Tuberculosis spreads through the air when a person with active pulmonary infection coughs or sneezes. Tuberculosis
  • Brucellosis Brucellosis Brucellosis (also known as undulant fever, Mediterranean fever, or Malta fever) is a zoonotic infection that spreads predominantly through ingestion of unpasteurized dairy products or direct contact with infected animal products. Clinical manifestations include fever, arthralgias, malaise, lymphadenopathy, and hepatosplenomegaly. Brucella/Brucellosis
  • Syphilis Syphilis Syphilis is a bacterial infection caused by the spirochete Treponema pallidum pallidum (T. p. pallidum), which is usually spread through sexual contact. Syphilis has 4 clinical stages: primary, secondary, latent, and tertiary. Syphilis
  • Cat scratch disease ( Bartonella henselae Bartonella henselae A species of gram-negative bacteria that is the etiologic agent of bacillary angiomatosis. This organism can also be a cause of cat-scratch disease in immunocompetent patients. Bartonella)
Parasitic
  • Toxoplasmosis Toxoplasmosis Toxoplasmosis is an infectious disease caused by Toxoplasma gondii, an obligate intracellular protozoan parasite. Felines are the definitive host, but transmission to humans can occur through contact with cat feces or the consumption of contaminated foods. The clinical presentation and complications depend on the host’s immune status. Toxoplasma/Toxoplasmosis
  • Malaria Malaria Malaria is an infectious parasitic disease affecting humans and other animals. Most commonly transmitted via the bite of a female Anopheles mosquito infected with microorganisms of the Plasmodium genus. Patients present with fever, chills, myalgia, headache, and diaphoresis. Plasmodium/Malaria
  • Babesiosis Babesiosis Babesiosis is an infection caused by a protozoa belonging to the genus, Babesia. The most common Babesia seen in the United States is B. microti, which is transmitted by the Ixodes tick. The protozoa thrive and replicate within host erythrocytes. Lysis of erythrocytes and the body’s immune response result in clinical symptoms. Babesia/Babesiosis

Other mechanisms of lymphocytosis

  • Redistribution of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology from bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types marrow or secondary lymphoid organs Lymphoid organs A system of organs and tissues that process and transport immune cells and lymph. Primary Lymphatic Organs: seen after splenectomy Splenectomy Surgical procedure involving either partial or entire removal of the spleen. Rupture of the Spleen
  • Decreased extravasation of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology from peripheral blood to lymphoid organs Lymphoid organs A system of organs and tissues that process and transport immune cells and lymph. Primary Lymphatic Organs: seen in pertussis Pertussis Pertussis, or whooping cough, is a potentially life-threatening highly contagious bacterial infection of the respiratory tract caused by Bordetella pertussis. The disease has 3 clinical stages, the second and third of which are characterized by an intense paroxysmal cough, an inspiratory whoop, and post-tussive vomiting. Pertussis (Whooping Cough) infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
  • Decreased cell death Cell death Injurious stimuli trigger the process of cellular adaptation, whereby cells respond to withstand the harmful changes in their environment. Overwhelmed adaptive mechanisms lead to cell injury. Mild stimuli produce reversible injury. If the stimulus is severe or persistent, injury becomes irreversible. Apoptosis is programmed cell death, a mechanism with both physiologic and pathologic effects. Cell Injury and Death from impaired apoptosis Apoptosis A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, I.e., DNA fragmentation. It is genetically-programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth. Ischemic Cell Damage: seen in some lymphoproliferative disorders
  • Unclear mechanisms: malignant thymoma Thymoma A neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. Although it is occasionally invasive, metastases are extremely rare. It consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin’s disease (previously termed granulomatous thymoma), should not be regarded as thymoma. Primary Lymphatic Organs

Pathophysiology

The pathophysiology depends on the underlying etiology. Increased production of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology may be due to a clonal process or a reactive process.

  • Clonal lymphocytosis:  
    • Seen in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with a lymphoproliferative disorder
    • Due to abnormal lymphocyte proliferation, usually owing to genetic mutations Genetic Mutations Carcinogenesis
    • Involves expansion of a single clone (monoclonal) or related cells 
  • Reactive lymphocytosis:
    • Seen in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship without a lymphoproliferative disorder
    • Due to “normal” lymphocyte proliferation in response to infection or inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation (i.e., the lymphocytosis is part of an immune response)
    • For further details on the immune response, see:
      • Innate immunity Innate immunity The capacity of a normal organism to remain unaffected by microorganisms and their toxins. It results from the presence of naturally occurring anti-infective agents, constitutional factors such as body temperature and immediate acting immune cells such as natural killer cells. Innate Immunity: Phagocytes and Antigen Presentation
      • Adaptive immunity
      • Cellular immunity Cellular immunity Manifestations of the immune response which are mediated by antigen-sensitized T-lymphocytes via lymphokines or direct cytotoxicity. This takes place in the absence of circulating antibody or where antibody plays a subordinate role. Squamous Cell Carcinoma (SCC)
      • Humoral immunity
    • Polyclonal expansion is seen in 1 or more subsets of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology (e.g., T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions, B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions, or NK cells NK cells A specialized subset of T-lymphocytes that exhibit features of innate immunity similar to that of natural killer cells. They are reactive to glycolipids presented in the context of the major histocompatibility complex (MHC) class I-like molecule, CD1D antigen. Lymphocytes: Histology).
    • Lymphocytosis should normalize < 2 months after resolution of the acute medical condition that triggered the reactive lymphocytosis.

Clinical Presentation

The clinical presentation Presentation The position or orientation of the fetus at near term or during obstetric labor, determined by its relation to the spine of the mother and the birth canal. The normal position is a vertical, cephalic presentation with the fetal vertex flexed on the neck. Normal and Abnormal Labor depends on the primary cause (i.e., infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease or lymphoproliferative disorders). Lymphocytosis can be an asymptomatic incidental finding.

Presentations associated with infection

Signs and symptoms may include:

  • Fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever
  • Lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy 
  • Hepatosplenomegaly Hepatosplenomegaly Cytomegalovirus
  • Upper respiratory symptoms:
    • Sore throat Sore throat Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis
    • Nasal congestion/ rhinorrhea Rhinorrhea Excess nasal drainage. Respiratory Syncytial Virus
    • Cough
  • Rashes Rashes Rashes are a group of diseases that cause abnormal coloration and texture to the skin. The etiologies are numerous but can include irritation, allergens, infections, or inflammatory conditions. Rashes that present in only 1 area of the body are called localized rashes. Generalized rashes occur diffusely throughout the body. Generalized and Localized Rashes
  • Fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia
  • Arthralgias and myalgias Myalgias Painful sensation in the muscles. Tick-borne Encephalitis Virus

Presentations associated with lymphoproliferative disorders

Signs and symptoms may include:

  • Low-grade fever Low-Grade Fever Erythema Infectiosum
  • Night sweats Night sweats Tuberculosis
  • Weight loss Weight loss Decrease in existing body weight. Bariatric Surgery
  • Diffuse or localized lymphadenopathy Localized Lymphadenopathy Lymphadenopathy
  • Splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly
  • Shortness of breath Shortness of breath Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea
  • Itching
  • Signs/symptoms related to bone marrow infiltration Bone Marrow Infiltration Multiple Myeloma
    • Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types: pallor, fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea
    • Thrombocytopenia Thrombocytopenia Thrombocytopenia occurs when the platelet count is < 150,000 per microliter. The normal range for platelets is usually 150,000-450,000/µL of whole blood. Thrombocytopenia can be a result of decreased production, increased destruction, or splenic sequestration of platelets. Patients are often asymptomatic until platelet counts are < 50,000/µL. Thrombocytopenia: easy bruising Easy bruising Chédiak-Higashi Syndrome or bleeding, purpura

Diagnosis and Management

The initial workup for lymphocytosis involves a comprehensive history and physical examination, CBC, and peripheral blood smear Peripheral Blood Smear Anemia: Overview and Types. If the diagnosis is still uncertain, or if findings are worrisome for malignancy Malignancy Hemothorax, clonality should be established using flow cytometry Flow cytometry Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake. X-linked Agammaglobulinemia.

Historical factors to consider

  • History or clinical evidence of infection and/or inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation, for example:
    • New-onset fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever and rash Rash Rocky Mountain Spotted Fever
    • Symptoms of upper respiratory infection Upper respiratory infection Rhinitis (URI)
    • History of arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis
    • Recent trauma
  • Clinical stability/acuity of illness
  • Rapidity of onset
  • Surgical or functional asplenia Functional Asplenia Asplenia
  • Medications

CBC findings

CBC findings associated with lymphocytosis include:

  • Changes from prior CBCs 
  • Eosinophils Eosinophils Granular leukocytes with a nucleus that usually has two lobes connected by a slender thread of chromatin, and cytoplasm containing coarse, round granules that are uniform in size and stainable by eosin. Innate Immunity: Phagocytes and Antigen Presentation or basophils Basophils Granular leukocytes characterized by a relatively pale-staining, lobate nucleus and cytoplasm containing coarse dark-staining granules of variable size and stainable by basic dyes. Innate Immunity: Phagocytes and Antigen Presentation, which may indicate:
    • Infection and/or inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation
    • Allergic conditions
    • Drug hypersensitivities
  • Neutrophils Neutrophils Granular leukocytes having a nucleus with three to five lobes connected by slender threads of chromatin, and cytoplasm containing fine inconspicuous granules and stainable by neutral dyes. Innate Immunity: Phagocytes and Antigen Presentation and/or monocytes Monocytes Large, phagocytic mononuclear leukocytes produced in the vertebrate bone marrow and released into the blood; contain a large, oval or somewhat indented nucleus surrounded by voluminous cytoplasm and numerous organelles. Innate Immunity: Phagocytes and Antigen Presentation, which may indicate:
    • Infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease and/or inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation
    • Severe medical stress
    • Asplenia Asplenia Asplenia is the absence of splenic tissue or function and can stem from several factors ranging from congenital to iatrogenic. There is a distinction between anatomic asplenia, which is due to the surgical removal of the spleen, and functional asplenia, which is due to a condition that leads to splenic atrophy, infarct, congestion, or infiltrative disease. Asplenia
  • Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types, which may indicate:
    • Bone marrow infiltration Bone Marrow Infiltration Multiple Myeloma
    • Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types of chronic disease associated with chronic inflammatory conditions or infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
    • Hemolytic anemia Hemolytic Anemia Hemolytic anemia (HA) is the term given to a large group of anemias that are caused by the premature destruction/hemolysis of circulating red blood cells (RBCs). Hemolysis can occur within (intravascular hemolysis) or outside the blood vessels (extravascular hemolysis). Hemolytic Anemia associated with CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia or LGL leukemia
  • Serious or multiple hematologic abnormalities (e.g., ALC > 50,000 cells/µL) require more urgent evaluation.

Peripheral blood smear Peripheral Blood Smear Anemia: Overview and Types

Peripheral blood smear Peripheral Blood Smear Anemia: Overview and Types for lymphocyte morphology may show:

  • Atypical lymphocytes Atypical lymphocytes Cytomegalovirus (also known as Downey cells):
    • Characteristics: more prominent nucleoli and more abundant cytoplasm
    • Seen in infectious Infectious Febrile Infant mononucleosis Mononucleosis Infectious mononucleosis (IM), also known as “the kissing disease,” is a highly contagious viral infection caused by the Epstein-Barr virus. Its common name is derived from its main method of transmission: the spread of infected saliva via kissing. Clinical manifestations of IM include fever, tonsillar pharyngitis, and lymphadenopathy. Mononucleosis due to EBV EBV Epstein-barr virus (EBV) is a linear, double-stranded DNA virus belonging to the herpesviridae family. This highly prevalent virus is mostly transmitted through contact with oropharyngeal secretions from an infected individual. The virus can infect epithelial cells and B lymphocytes, where it can undergo lytic replication or latency. Epstein-Barr Virus or CMV, toxoplasmosis Toxoplasmosis Toxoplasmosis is an infectious disease caused by Toxoplasma gondii, an obligate intracellular protozoan parasite. Felines are the definitive host, but transmission to humans can occur through contact with cat feces or the consumption of contaminated foods. The clinical presentation and complications depend on the host’s immune status. Toxoplasma/Toxoplasmosis, and viral hepatitis
  • Lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology with hair-like projections → seen in hairy cell leukemia Hairy cell leukemia Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia
  • Lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology with azurophilic granules Azurophilic granules Myeloperoxidase Deficiency → seen in LGL leukemia
  • Lymphoblasts → seen in ALL
  • Smudge cells Smudge Cells Chronic Lymphocytic Leukemia and lymphoblasts → seen in CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia
Peripheral blood smear with occasional small lymphocytes

Peripheral blood smear Peripheral Blood Smear Anemia: Overview and Types showing a lymphocyte with hair-like cytoplasmic projections (known as “ hairy cells Hairy Cells Hairy Cell Leukemia”) in hairy cell leukemia Hairy cell leukemia Hairy cell leukemia (HCL) is a rare, chronic, B-cell leukemia characterized by the accumulation of small mature B lymphocytes that have “hair-like projections” visible on microscopy. The abnormal cells accumulate in the peripheral blood, bone marrow (causing fibrosis), and red pulp of the spleen, leading to cytopenias. Hairy Cell Leukemia

Image: “ Peripheral blood smear Peripheral Blood Smear Anemia: Overview and Types” by Department of Pathology and Laboratory Medicine and Department of Hematology-Oncology, Tufts Medical Center, Tufts University Medical School, Washington Street 800, Boston, MA 02111, USA. License: CC BY 3.0

Flow cytometry Flow cytometry Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake. X-linked Agammaglobulinemia

  • Determines the clonality and immunophenotype of a lymphocytosis 
  • Important in diagnosing malignancy Malignancy Hemothorax: All malignant lymphocytosis is clonal (though not all clonal lymphocytosis is malignant).
  • Indications:
    • Suspicion for malignancy Malignancy Hemothorax (e.g., lymphoblasts on peripheral smear)
    • ALC > 30,000 cells/µL without a known cause 
    • Lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy
    • Hepatosplenomegaly Hepatosplenomegaly Cytomegalovirus
    • Cytopenias Cytopenias IPEX Syndrome

Additional tests

Additional tests may be required based on the provisional diagnosis:

  • Viral serologies
  • Bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types marrow biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma
  • Imaging tests
  • Specialized tests for clonality include:
    • Flow cytometry Flow cytometry Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake. X-linked Agammaglobulinemia (first-line test)
    • Molecular and genetic testing Genetic Testing Detection of a mutation; genotype; karyotype; or specific alleles associated with genetic traits, heritable diseases, or predisposition to a disease, or that may lead to the disease in descendants. It includes prenatal genetic testing. Myotonic Dystrophies (e.g., PCR PCR Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR) and DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure sequencing)
    • Chromosome Chromosome In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. Basic Terms of Genetics analysis

Persistent lymphocytosis

If lymphocytosis persists for ≥ 3 months and the cause is unclear, a further workup should be completed. This workup should include:

  • Serial CBCs with differential 
  • Chemistries (to evaluate liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy and kidney function)
  • Erythrocyte sedimentation rate Erythrocyte Sedimentation Rate Soft Tissue Abscess ( ESR ESR Soft Tissue Abscess) and CRP
  • Peripheral blood smear Peripheral Blood Smear Anemia: Overview and Types (if not already done)
  • Peripheral blood flow cytometry Flow cytometry Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake. X-linked Agammaglobulinemia (if not already done)

Management

Management of lymphocytosis is related to the underlying etiology. 

  • Infectious etiologies Infectious Etiologies High-Risk Headaches
    • Usually transient and asymptomatic: In most cases, lymphocytosis resolves on its own after resolution of the infection.
    • Observation and supportive care
    • Antibiotics as normally indicated for bacterial infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease.
  • Lymphoproliferative disorders:
    • Management by a hematology-oncology specialist
    • Management may involve:
      • Chemotherapy Chemotherapy Osteosarcoma
      • Immunotherapy
      • Radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma therapy
      • Bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types marrow transplantation

Differential Diagnosis

  • Infectious Infectious Febrile Infant causes (see table under “Etiology and Pathophysiology”)
  • ALL: cancer of the blood and bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types marrow resulting from abnormal proliferation of lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology. There are > 10 subtypes of ALL. ALL is rare, with < 6000 adults and children diagnosed in the United States each year, though ALL is the most common childhood cancer.
  • CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia: most common leukemia in adults. CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia is a monoclonal B-cell proliferation that infiltrates the bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types marrow and/or lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy. The B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions arrest before maturation, and many patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship have hypogammaglobulinemia Hypogammaglobulinemia Selective IgA Deficiency resulting in recurrent infections Recurrent infections Common Variable Immunodeficiency (CVID). CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia is mainly found on incidental blood work showing lymphocytosis, though patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship may also present with lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy, hepatosplenomegaly Hepatosplenomegaly Cytomegalovirus, or skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions manifestations. Peripheral blood smears show smudge cells Smudge Cells Chronic Lymphocytic Leukemia
  • MBL: condition characterized by elevation of monoclonal B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions persisting ≥ 3 months. The monoclonal B cells B cells Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. B cells: Types and Functions are phenotypically similar to those in CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia (though found at levels below the threshold Threshold Minimum voltage necessary to generate an action potential (an all-or-none response) Skeletal Muscle Contraction for CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia), in the absence of other features typically found in lymphoproliferative disorders (e.g., splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly, lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy, or other cytopenias Cytopenias IPEX Syndrome). MBL may progress to CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia.
  • Congenital Congenital Chorioretinitis polyclonal B-cell lymphocytosis: rare congenital Congenital Chorioretinitis disorder of children that presents in infancy with significant lymphocytosis and splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly due to polyclonal B-cell expansion. The lymphocytosis may become indistinguishable from CLL CLL Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Chronic Lymphocytic Leukemia later in life. 
  • Persistent polyclonal B-cell lymphocytosis: rare syndrome characterized by polyclonal B-cell expansion, splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly, and/or lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy. This disorder is typically diagnosed in young to middle-aged women who smoke cigarettes. The pathogenesis is unknown.
  • LGL leukemia: relatively rare atypical lymphocytosis characterized by large lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology with slightly eccentric nuclei and abundant pale-blue cytoplasm containing many azurophilic granules Azurophilic granules Myeloperoxidase Deficiency. Phenotypically, these are clonal lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology. These patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship usually present in middle age with splenomegaly Splenomegaly Splenomegaly is pathologic enlargement of the spleen that is attributable to numerous causes, including infections, hemoglobinopathies, infiltrative processes, and outflow obstruction of the portal vein. Splenomegaly and autoimmune manifestations. While there may be an absolute lymphocytosis in LGL leukemia, there is frequently a neutropenia Neutropenia Neutrophils are an important component of the immune system and play a significant role in the eradication of infections. Low numbers of circulating neutrophils, referred to as neutropenia, predispose the body to recurrent infections or sepsis, though patients can also be asymptomatic. Neutropenia and/or normal total lymphocyte count with an increased percentage of cytotoxic Cytotoxic Parvovirus B19 T cells T cells Lymphocytes responsible for cell-mediated immunity. Two types have been identified – cytotoxic (t-lymphocytes, cytotoxic) and helper T-lymphocytes (t-lymphocytes, helper-inducer). They are formed when lymphocytes circulate through the thymus gland and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. T cells: Types and Functions.
  • Malignant thymoma Thymoma A neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. Although it is occasionally invasive, metastases are extremely rare. It consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin’s disease (previously termed granulomatous thymoma), should not be regarded as thymoma. Primary Lymphatic Organs: malignant tumor Tumor Inflammation of the thymus Thymus A single, unpaired primary lymphoid organ situated in the mediastinum, extending superiorly into the neck to the lower edge of the thyroid gland and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat. Lymphatic Drainage System: Anatomy gland. Malignant thymoma Thymoma A neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. Although it is occasionally invasive, metastases are extremely rare. It consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin’s disease (previously termed granulomatous thymoma), should not be regarded as thymoma. Primary Lymphatic Organs typically affects middle-aged adults and may be associated with paraneoplastic autoimmune syndromes. The cause of the lymphocytosis is unclear, but the morphology appears normal. This condition is associated with polyclonal T-cell lymphocytosis and resolves following successful treatment of the tumor Tumor Inflammation.

References

  1. Davids, M.S. (2020). Approach to the adult with lymphocytosis or lymphocytopenia.  UpToDate.  Accessed April 22, 2021, from https://www.uptodate.com/contents/approach-to-the-adult-with-lymphocytosis-or-lymphocytopenia
  2. Coates, T.D. (2020). Approach to the child with lymphocytosis or lymphocytopenia.  UpToDate. Accessed April 22, 2021, from https://www.uptodate.com/contents/approach-to-the-child-with-lymphocytosis-or-lymphocytopenia
  3. Teggatz, J.R., Parkin, J., Peterson, L. (1987). Transient atypical lymphocytosis in patients with emergency medical conditions. Archives of Pathology and Laboratory Medicine 111:712–714.
  4. Snow, A.L., Xiao, W., et al. (2012). Congenital B cell lymphocytosis explained by novel germline CARD11 mutations. Journal of Experimental Medicine 209:2247–2261.
  5. Dasanu, C.A., Codreanu, I. (2012). Persistent polyclonal B-cell lymphocytosis in chronic smokers: more than meets the eye. Connecticut Medicine 76(2):69–72.

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