Basics
Description
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 are 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
Epidemiology
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 early during infancy or childhood
The incidence and prevalence of secondary polycythemias depend on the respective underlying conditions.
Risk Factors
Genetics
- PFCP: autosomal dominant
- Chuvash polycythemia: autosomal recessive
- 2,3-diphosphoglycerate (DPG) mutase deficiency: autosomal recessive
General Prevention
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.
Pathophysiology
- 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 alpha or beta globin chains leading to increased oxygen affinity and decreased oxygen delivery to tissues
- 2,3-DPG mutase deficiency: rare defect that leads to deficiency of 2,3-DPG. Because 2,3-DPG promotes the release of oxygen from hemoglobin, deficiency leads to 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 genes von Hippel Lindau (VHL) are common in certain ethnic groups (Chuvash polycythemia). Hypoxia-inducible factor 2 (HIF2) and proline hydroxylase (PHD2) have also been described.
- EPO-producing tumors: renal cell carcinoma, hepatocellular carcinoma, hemangioblastoma, pheochromocytoma, and uterine fibroids
Diagnosis
History
- 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.
- Gender
- Weight: Obesity is associated with obstructive sleep apnea.
- Dehydration
- Diuretic use or abuse
- Severe diarrhea
- Hyperviscosity
- Headache, dizziness, syncope, transient blindness, history of thrombosis
- Symptoms concerning for congenital heart disease or chronic pulmonary disease:
- Cyanosis
- Decreased exercise tolerance
- Shortness of breath
- Dyspnea on exertion
- Pruritus
- Seen with polycythemia vera
- 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
- Smoking (tobacco or marijuana)
- Drug use including steroids, EPO, diuretics
- Family history
- High hematocrit, hyperviscosity, or need for phlebotomy
- Family members with similar symptoms may also indicate concurrent exposure to carbon monoxide
Physical Exam
Signs and symptoms:
- Cyanosis
- Plethora
- Clubbing
- Cardiac murmurs or bruits
- Dehydration
- Splenomegaly
Alert
- 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.
Diagnostic Tests & Interpretation
Lab
- 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. Leukocytosis and thrombocytosis may be noted in myelodysplastic disorders.
- 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 significant overlap in EPO levels between the two categories
- Further investigation
- Hemoglobin dissociation curve P50: the partial pressure of oxygen at which hemoglobin is 50% saturated (must be performed on fresh whole blood samples)
- Hemoglobin electrophoresis: Normal results do not rule out the presence of high oxygen-affinity hemoglobin, as many can comigrate with normal hemoglobins.
- Molecular genetic analysis of globin genes
- 2,3-DPG level
- Testosterone level
- Genetic testing for JAK2 V617F mutation
- RBC mass measurement using isotope dilution methods
- Erythroid progenitor studies for erythroid burst-forming units (BFU-E) that grow independent of EPO
Imaging
- Chest radiograph: initial evaluation for chronic pulmonary disease
- Abdominal ultrasound: evaluation for abdominal tumors
Diagnostic Procedures/Other
- EKG and echocardiogram: for clinical findings concerning for congenital heart disease
- Polysomnography sleep study: for clinical findings consistent with sleep apnea
- If myeloproliferative neoplasm is suspected, bone marrow aspirate and biopsy with cytogenetics should be performed. Analysis of erythroid progenitors through colony-forming assays.
Differential Diagnosis
- Primary polycythemia
- Polycythemia vera
- Primary familial and congenital polycythemia
- Secondary polycythemia
- High altitudes
- 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-DPG mutase deficiency
- Methemoglobinemia
- Carbon monoxide poisoning
- EPO-producing tumors: renal cell carcinoma, hepatocellular carcinoma, hemangioblastoma, pheochromocytoma, uterine fibroids
- Status-post renal 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
- Dehydration
Treatment
Medication
Primary polycythemia should be managed by a hematologist. Certain medications, such as hydroxyurea and interferon alpha, may be considered.
Additional Treatment
General Measures
- Most asymptomatic patients with secondary polycythemia require no additional therapy other than management of their underlying condition.
- Due to the long-term leukemic potential of many chemotherapy agents, many pediatric patients with primary polycythemia are managed with phlebotomy only. 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.
Issues for Referral
Unexplained cyanosis, symptoms concerning for hyperviscosity, or persistent elevation in hematocrit that is not related to dehydration or neonatal etiologies
Ongoing Care
Follow-up Recommendations
Patient Monitoring
Periodic laboratory follow-up depending on the etiology of polycythemia. Monitor for the following:
- Headache, dizziness, or syncope
- Decreased exercise tolerance, shortness of breath, or dyspnea on exertion
- Stroke or thrombosis
Prognosis
Depends on underlying condition:
- Polycythemia vera: guarded as may progress to acute leukemia
- High oxygen-affinity hemoglobinopathies: good
- Other secondary polycythemias: depend on underlying condition (e.g., poor prognosis for Eisenmenger syndrome due to progressive pulmonary hypertension and cor pulmonale)
Complications
From hyperviscosity:
- Decreased exercise tolerance, dyspnea on exertion, transient visual disturbances, and mental status changes
- Stroke or other thrombosis
Additional Reading
- Cario H, McMullin MF, Pahl HL. Clinical and hematological presentation of children and adolescents with polycythemia vera. Ann Hematol. 2009;88(8):713 " 719. [View Abstract]
- Messinezy M, Pearson TC. The classification and diagnostic criteria of the erythrocytoses (polycythemias). Clin Lab Haematol. 1999;21(5):309 " 316. [View Abstract]
- Ozek E, Soll R, Schimmel MS. Partial exchange transfusion to prevent neurodevelopmental disability in infants with polycythemia. Cochrane Database Syst Rev. 2010;(1):CD005089. [View Abstract]
- Prchal JT. Polycythemia vera and other primary polycythemias. Curr Opin Hematol. 2005;12(2):112 " 116. [View Abstract]
- Sarkar S, Rosenkrantz TS. Neonatal polycythemia and hyperviscosity. Semin Fetal Neonatal Med. 2008;13(4):248 " 255. [View Abstract]
- Tefferi A. Polycythemia vera and essential thrombocythemia: 2012 update on diagnosis, risk stratification, and management. Am J Hematol. 2012;87(3):285 " 293. [View Abstract]
Codes
ICD09
- 238.4 Polycythemia vera
- 289.0 Polycythemia, secondary
- 776.4 Polycythemia neonatorum
ICD10
- D45 Polycythemia vera
- D75.1 Secondary polycythemia
- P61.1 Polycythemia neonatorum
SNOMED
- 109992005 Polycythemia vera (disorder)
- 127066000 Familial polycythemia vera (disorder)
- 32984002 Neonatal polycythemia (disorder)
FAQ
- 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.