Complete Blood Count

Nursing Knowledge

Complete Blood Count

A complete blood count (CBC) is a common lab test that provides information about the types and numbers of cells in the blood. CBC is an essential tool for healthcare professionals, especially nurses, to diagnose and monitor various medical conditions, such as infections, anemia, leukemia, and bleeding disorders. Keep reading for a guide on the different types of blood cells, their functions, reference ranges, and what abnormal results may indicate.
Last updated: December 4, 2023

Table of contents

What is a complete blood count? 

A complete blood count (CBC) is a common blood test that provides detailed information about three types of cells in the blood: red blood cells (RBCs), white blood cells (WBCs), and platelets. 

A CBC is obtained via a blood sample in a purple top tube and provides valuable information about the overall health status and can be used to diagnose and monitor many different conditions, including anemia, infection, clotting disorders, leukemia, and response to treatment. It’s a standard test that’s often part of routine health examinations or performed to help diagnose symptoms.

Overview: types of cells in the blood 

Table: Blood cell types

White blood cells (leukocytes, WBC)Fight infections by attacking bacteria, viruses, germs that invade the body13–20 days (destroyed in the lymphatic system)
Red blood cells (RBC)Carry hemoglobin that binds to oxygen, carry O2 to tissue and CO2 to lungs to be exhaled120 days
Platelets20% of the diameter of a RBC, principal function is to prevent bleeding8–9 days

Complete blood count: normal ranges chart 

Table: Normal cell counts in the blood

Type of cellReference range (can vary depending on source)
WBC5000–10,000 cells/mm3
RBCMale: 4.7–6.1 × 106/μL, elderly: 4.7–6.1 × 1012/L, female: 4.2–5.4 × 106/μL, elderly: 4.2–5.4 × 1012/L 
Hemoglobin (HgB)Male: 14–18 g/dL (140–180 g/L), female: 12–16 g/dL (120–160 g/L)
Hematocrit (Hct)Male: 42%–50% (0.40–0.50), female: 37%–47% (0.37–0.47)
Platelet count150,000–400,000/mm3 (150 to 400 × 109/L)

Complete blood count interpretations: How to read a CBC blood test 

Cell count values may vary based on the laboratory, population, or age and overall health of the client. Any abnormalities should be correlated with clinical signs, symptoms, and other diagnostic information. 

Indications of decreased cell counts 

Table: Indications of decreased cell counts

Type of cellIndication
WBCInfection, liver or spleen conditions, cancer
RBCHemorrhage, anemia, cancer, malnutrition
Hemoglobin (Hgb)Any abnormalities in Hgb can indicate concerns in the blood‘s oxygen-carrying capacity. 
Hematocrit (Hct)Low levels of iron, heavy menses, anemia
Platelet countHigher risk for bleeding

Indications of increased cell counts 

Table: Indications of increased cell counts

Type of cellIndication
WBCInfections, allergic reactions, autoimmune conditions
RBCDehydration, heart or lung disease, polycythemia vera
Hemoglobin (Hgb)Any abnormalities in Hgb can indicate concerns in the blood‘s oxygen-carrying capacity. 
Hematocrit (Hct)Polycythemia vera, dehydration, shock
Platelet countHigher risk for blood clots

What CBC blood test indicates cancer? 

A Complete Blood Count (CBC) alone does not diagnose cancer, but it can show abnormalities that may be indicative of cancer or various benign conditions as well. 

For example, unusually high or low WBC counts can indicate leukemia or lymphoma. Some cancers can cause elevated platelet counts, and a low red blood cell count can be a sign of certain cancers as well. 

Do you need to fast for a CBC blood test? 

Clients do not need to be advised to fast before a CBC blood test.


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Overview of CBC values and types of cells in the blood

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