Overview

Definitions

• Neonatal polycythemia (absolute polycythemia): increased erythrocyte mass defined as hematocrit (HCT) > 65% or hemoglobin (Hb) > 22 g/dL
• Hemoconcentration (relative polycythemia): a decrease in plasma volume resulting in an increased concentration of  erythrocytes Erythrocytes Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes

Epidemiology

•  1%–2% of children born at sea level 
•  5% of children born at high altitudes

Etiology

• Increased fetal erythropoiesis Erythropoiesis Erythropoiesis starts with hematopoietic stem cells, which develop into lineage-committed progenitors and differentiate into mature RBCs. The process occurs in stages, and extrusion of the nuclei and organelles occurs prior to maturation. Thus, mature RBCs lack nuclei and have a biconcave shape. Erythrocytes
  • Placental insufficiency
    • Preeclampsia
    • Maternal hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
    • Chronic or recurrent placental abruption
    • Maternal cyanotic heart or severe pulmonary disease
    • Postdate pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-HCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care
    • Maternal smoking
    • Mother residing at a high altitude
  • Endocrinopathies
    • Poorly controlled maternal diabetes
    • Congenital thyrotoxicosis Thyrotoxicosis Thyrotoxicosis refers to the classic physiologic manifestations of excess thyroid hormones and is not synonymous with hyperthyroidism, which is caused by sustained overproduction and release of T3 and/or T4. Graves' disease is the most common cause of primary hyperthyroidism, followed by toxic multinodular goiter and toxic adenoma. Thyrotoxicosis and Hyperthyroidism
  • Genetic disorders
    • Trisomies 13, 18, 21
    • Beckwith-Weidemann syndrome
  • Adrenal hyperplasia
  • Perinatal asphyxia
  • Intrauterine growth restriction
  • Intrauterine chronic hypoxia
• Passive erythrocyte transfusion
  • Placental-fetal transfusion (delayed cord clamping, newborn Newborn A neonate, or newborn, is defined as a child less than 28 days old. A thorough physical examination should be performed within the first 24 hours of life to identify abnormalities and improve outcomes by offering timely treatment. Physical Examination of the Newborn held below mother’s level before cord clamping)
  • Feto-fetal transfusion (twin-twin transfusion syndrome)
  • Mother-fetal hemorrhage

Pathophysiology

• Blood viscosity increases with increased HCT.
• Hyperviscosity increases resistance to blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure, especially in the microcirculation.
• Decreased blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure increases risk for thrombosis and hypoperfusion.
• Lung hypoperfusion causes further tissue hypoxia.

Clinical Presentation

• The majority of cases are asymptomatic. 
• If present, symptoms usually appear by 2 hours after birth.
• Most characteristic findings: plethora and ruddiness
• Neurologic manifestations:
  • Poor feeding and lethargy
  • Irritability, jitteriness, and tremor
  • Seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures
  • Cerebrovascular accidents
• Cardiopulmonary manifestations:
  • Respiratory distress and tachypnea
  • Cyanosis and apnea
• Gastrointestinal manifestations:
  • Necrotizing enterocolitis Necrotizing enterocolitis Necrotizing enterocolitis (NEC) is an intestinal inflammatory process that can lead to mucosal injury and necrosis. The condition is multifactorial, with underlying risk factors that include prematurity and formula feeding. The clinical presentation varies in severity from feeding intolerance, acute findings on abdominal exam, and systemic symptoms. Necrotizing Enterocolitis with feeding intolerance, abdominal distension and tenderness, rectorrhagia, bradycardia, and apnea
• Genitourinary manifestations:
  • Oliguria
  • Hematuria
  • Priapism

Diagnosis and Management

Laboratory studies

• Diagnosis is confirmed with a complete blood count showing HCT > 65% or Hb > 22 mg/dL (capillary values must be confirmed by venous values).
• Other common findings:
  • 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 
  • Hypoglycemia Hypoglycemia Hypoglycemia is an emergency condition defined as a serum glucose level ≤ 70 mg/dL (≤ 3.9 mmol/L) in diabetic patients. In nondiabetic patients, there is no specific or defined limit for normal serum glucose levels, and hypoglycemia is defined mainly by its clinical features. Hypoglycemia
  • Hyperbilirubinemia 
  • Hypocalcemia Hypocalcemia Hypocalcemia, a serum calcium < 8.5 mg/dL, can result from various conditions. The causes may include hypoparathyroidism, drugs, disorders leading to vitamin D deficiency, and more. Calcium levels are regulated and affected by different elements such as dietary intake, parathyroid hormone (PTH), vitamin D, pH, and albumin. Presentation can range from an asymptomatic (mild deficiency) to a life-threatening condition (acute, significant deficiency). Hypocalcemia
  • Hypoxia and acidosis in arterial blood gas

Imaging studies

• May be required to exclude differential diagnoses or complications
• Cranial ultrasound, computed tomography (CT) scan, or magnetic resonance imaging (MRI) to rule out cerebrovascular accident Cerebrovascular accident An ischemic stroke (also known as cerebrovascular accident) is an acute neurologic injury that occurs as a result of brain ischemia; this condition may be due to cerebral blood vessel occlusion by thrombosis or embolism, or rarely due to systemic hypoperfusion. Ischemic Stroke (CVA) including intracranial hemorrhage
• Echocardiography to rule out cardiopulmonary disorders
• Chest X-ray to rule out transient tachypnea of the newborn Newborn A neonate, or newborn, is defined as a child less than 28 days old. A thorough physical examination should be performed within the first 24 hours of life to identify abnormalities and improve outcomes by offering timely treatment. Physical Examination of the Newborn, respiratory distress syndrome, pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia
• Abdominal X-ray or CT scan for signs of necrotizing enterocolitis

Management

• Careful monitoring for vital signs, hypoglycemia, hypoxia, electrolyte abnormalities, hyperbilirubinemia, and urine output
• Mainstay of treatment is partial exchange transfusion (PET):
  • PET involves slowly removing blood and infusing normal saline.
  • Asymptomatic patients with HCT > 75% may benefit from PET.
  • Symptomatic patients with HCT 60%–65%: consider alternative diagnoses
  • Symptomatic patients with HCT > 65%: consider PET
  • It is unclear whether polycythemia or PET have long-term health consequences.