Polycythemia (sometimes referred to as erythrocytosis) is defined as an absolute increase in red blood cell (RBC) mass, most commonly suspected in the context of an elevated hemoglobin, hematocrit, or RBC count. Use of age- and gender-based norms is critical, as they fluctuate throughout childhood. Polycythemia can be categorized as follows:
- Primary polycythemia: Defect within erythroid progenitors, resulting in overproduction of RBCs. Serum erythropoietin (EPO) levels are usually low.
- Secondary polycythemia: stimulation of erythrocyte production by an increased level of EPO, which is either elevated appropriately in response to hypoxia or elevated inappropriately due to an EPO-producing tumor or exogenous administration
- Relative polycythemia: elevated hemoglobin, hematocrit, or RBC count without a true increase in RBC mass, often caused by decreased plasma volume in the setting of dehydration
Primary polycythemias are very rare in children:
- Myeloproliferative neoplasms, including polycythemia vera (PV): Vast majority of cases occur in older adults, but cases of childhood PV have been described.
- Primary familial and congenital polycythemia (PFCP): very rare but presents during infancy or childhood
- The incidence and prevalence of secondary polycythemias depend on the respective underlying conditions.
Inherited polycythemias are very rare:
- PFCP: autosomal dominant
- Chuvash polycythemia: autosomal recessive disorder affecting individuals from the Chuvash Republic in Russia
- 2,3-bisphosphoglycerate (2,3-BPG) mutase deficiency: autosomal recessive
There are no preventive measures for conditions of primary polycythemia. Treatment of underlying conditions, such as correction of congenital heart disease, will prevent the development of secondary polycythemia.
- Primary polycythemias:
- PV: myeloproliferative neoplasm arising from a clonal population of abnormal hematopoietic progenitor cells with EPO-independent proliferation. EPO levels are usually low. The mutation JAK2 V617F is found in the vast majority of cases.
- PFCP: Erythroid progenitors are hypersensitive to EPO. Some families have a mutation in the EPO receptor (EPO-R).
- Secondary polycythemias:
- High altitude: compensation for low atmospheric oxygen pressure
- Chronic pulmonary disease or hypoventilation: compensation for inadequate oxygenation
- Cyanotic heart disease and arteriovenous malformations: right-to-left cardiac or extracardiac shunting, resulting in desaturation of arterial blood
- High oxygen-affinity hemoglobinopathies: mutation in either α- or β-globin chains leading to increased oxygen affinity and decreased oxygen delivery to tissues.
- 2,3-BPG mutase deficiency: rare defect that leads to deficiency of 2,3-BPG and decreased oxygen delivery to tissues
- Methemoglobinemia: elevated levels of Fe3+ hemoglobin, which has an increased affinity for oxygen compared to Fe2+ hemoglobin
- Carboxyhemoglobinemia: Carbon monoxide binds to hemoglobin preferentially compared to oxygen.
- Hypoxia-sensing pathway defects: Mutations in the gene von Hippel Lindau (VHL) are common in certain ethnic groups (Chuvash polycythemia).
- EPO-producing tumors: renal cell carcinoma, hepatocellular carcinoma, hemangioblastoma, pheochromocytoma, and uterine fibroids
- Age of onset:
- Neonates, who are born to mothers with preeclampsia or diabetes, are small for gestational age, undergo delayed cord clamping, or have certain chromosomal abnormalities (e.g., Down syndrome), are at increased risk for polycythemia during the neonatal period.
- Obesity is associated with obstructive sleep apnea.
- Diuretic use or abuse
- Severe diarrhea
- Headache, dizziness, syncope, transient blindness, history of thrombosis
- Symptoms concerning for congenital heart disease or chronic pulmonary disease:
- Decreased exercise tolerance
- Shortness of breath
- Dyspnea on exertion
- Seen with PV
- Sleep history:
- Snoring, nocturnal apnea, mouth breathing, excessive daytime sleepiness, behavioral problems concerning for obstructive sleep apnea
- Living situation:
- High altitude
- Older house with fuel-burning heaters
- Cigarette exposure
- Social history:
- Drug use including steroids, EPO, diuretics
- Family history:
- High hematocrit, hyperviscosity, or need for phlebotomy
- Household members with similar symptoms may also indicate concurrent exposure to carbon monoxide.
Signs and symptoms:
- Pulse oximetry
- Cardiac murmurs or bruits
- Fingerstick hematocrit: Squeezing the finger to collect a specimen may give a falsely elevated hematocrit.
- Capillary hematocrit: often higher than venous hematocrit
- Dehydration during blood draw may result in relative polycythemia due to decreased plasma volume.
- Pao2 is only interpretable with an arterial blood gas.
- Primary polycythemia
- Secondary polycythemia
- High altitude
- Chronic pulmonary disease
- Hypoventilation: obstructive sleep apnea, neuromuscular disorders, severe obesity (Pickwickian syndrome), or congenital central hypoventilation syndrome
- Right-to-left cardiac shunts
- Arteriovenous malformations
- High oxygen-affinity hemoglobinopathies
- 2,3-BPG mutase deficiency
- Carbon monoxide poisoning
- EPO-producing tumors: renal cell carcinoma, hepatocellular carcinoma, hemangioblastoma, pheochromocytoma, uterine fibroids
- Status—postrenal transplant
- Exogenous testosterone or EPO: competitive athletes
- Cobalt poisoning: Homemade beer may contain cobalt.
- Neonatal polycythemia
- Preeclampsia or gestational hypertension
- Small for gestational age
- Gestational diabetes
- Delayed cord clamping
- Placental transfusion
- Twin-to-twin transfusion
- Relative polycythemia
- Cigarette smoking
Diagnostic Tests and Interpretation
- Many patients may be asymptomatic with polycythemia noted on routine screening.
- Initial workup should include the following:
- CBC with differential: Polycythemia may be associated with abnormalities in other lineages.
- Arterial blood gas with co-oximetry: Pao2 may be low in cardiopulmonary diseases. Co-oximetry allows for evaluation of carboxyhemoglobin and methemoglobin levels. Half-life of carboxyhemoglobin is 4 hours, so testing should be timed to accurately reflect exposures.
- BUN, serum creatinine, and urinalysis to evaluate renal function
- Serum EPO may be helpful in distinguishing primary from secondary polycythemia, but there is significant overlap in EPO levels between the two categories.
- Further investigation:
- Oxygen dissociation p50: the partial pressure of oxygen at which hemoglobin is 50% saturated
- Hemoglobin electrophoresis: Normal results do not rule out the presence of high oxygen-affinity hemoglobin, as many abnormal hemoglobins can comigrate with normal hemoglobins. If there is a high index of suspicion, consider molecular genetic analysis of globin genes.
- 2,3-BPG level
- Testosterone level
- Genetic testing for JAK2 V617F mutation
- Chest radiograph: for clinical findings concerning for chronic pulmonary disease
- Abdominal ultrasound: for clinical findings concerning for abdominal tumors
- EKG and echocardiogram: for clinical findings concerning for congenital heart disease
- Polysomnography sleep study: for clinical findings concerning for sleep apnea
- If myeloproliferative neoplasm is suspected, bone marrow aspirate and biopsy with cytogenetics should be performed.
- Most asymptomatic patients with secondary polycythemia require no additional therapy other than management of their underlying condition.
- Pediatric patients with primary polycythemia are managed with phlebotomy alone. Low-dose aspirin may be considered to reduce thrombosis risk.
- In neonatal polycythemia, partial exchange transfusion should be considered based on symptoms and degree of polycythemia.
Primary polycythemia should be managed by a hematologist. Certain medications, such as hydroxyurea and interferon-α, may be considered.
Issue for Referral
Unexplained cyanosis, symptoms concerning for hyperviscosity, or persistent elevation in hematocrit that is not related to dehydration or neonatal etiologies
Periodic laboratory follow-up depending on the etiology of polycythemia. Monitor for the following:
- Headache, dizziness, or syncope
- Blurred vision or transient vision loss
- Decreased exercise tolerance, shortness of breath, or dyspnea on exertion
- Stroke or thrombosis
Depends on underlying condition:
- PV: guarded as may progress to acute leukemia
- High oxygen-affinity hemoglobinopathies: excellent
- Other secondary polycythemias: depends on underlying condition
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- 238.4 Polycythemia vera
- 289.0 Polycythemia, secondary
- 776.4 Polycythemia neonatorum
- D45 Polycythemia vera
- D75.1 Secondary polycythemia
- P61.1 Polycythemia neonatorum
- 109992005 Polycythemia vera (disorder)
- 127066000 Familial polycythemia vera (disorder)
- 32984002 Neonatal polycythemia (disorder)
- Q: What are common causes of polycythemia in the pediatric population?
- A: Secondary polycythemias. In particular, neonates and patients with cyanotic heart disease commonly present with polycythemia.
- Q: What are common causes of relative polycythemia?
- A: Dehydration and heavy cigarette smoking have been associated with decreased plasma volume and relative polycythemia.
- Q: When should a child with polycythemia be referred to a pediatric hematologist?
- A: The child should be referred to a pediatric hematologist if there are symptoms concerning for hyperviscosity or if the elevation in hematocrit is persistent and not clearly due to dehydration or neonatal etiologies.
Benjamin J. Huang, MD
Tannie Huang, MD
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