Polycythemia Vera and Secondary Erythrocytosis

Diagnostic Criteria and Testing

The World Health Organization recommends that a diagnosis of polycythemia vera be made based on either both major criteria (hemoglobin >16.5 g/dL in women or >18.5 g/dL in men PLUS JAK2 mutation) plus one minor criterion, or the first major criterion plus two minor criteria, according to the American Society of Hematology 1
JAK2 mutation testing should be ordered immediately as the first-line diagnostic test, with JAK2V617F found in up to 97% of polycythemia vera cases, as suggested by the National Comprehensive Cancer Network 1, 2
Minor criteria include bone marrow hypercellularity with trilineage growth, subnormal erythropoietin level, or endogenous erythroid colony formation, as defined by the International Working Group for Myeloproliferative Neoplasms 1

Chronic obstructive pulmonary disease (COPD) causes tissue hypoxia that stimulates erythropoietin production, leading to compensatory erythrocytosis, as stated by the American Thoracic Society 1
Obstructive sleep apnea produces nocturnal hypoxemia that drives erythropoietin production and should be evaluated with sleep study if suspected, according to the American Academy of Sleep Medicine 1
Smoking causes "smoker's polycythemia" through chronic carbon monoxide exposure, which creates tissue hypoxia and stimulates erythropoietin production; this resolves with smoking cessation, as recommended by the US Surgeon General 1
High altitude residence causes physiological increases in hemoglobin levels, with specific adjustments needed based on elevation (e.g., +1.9 g/dL at 3,000 meters), as suggested by the European Respiratory Society 1

Dehydration is the most common cause of elevated hematocrit and should be assessed first by reviewing fluid intake history and recent losses, as stated by the American Society of Nephrology 2
Diuretic use can cause plasma volume depletion leading to relative polycythemia without true increase in red cell mass, as reported by the European Society of Cardiology 1

Complete blood count with red cell indices, reticulocyte count, and manual differential should be ordered immediately to characterize the elevations, as recommended by the College of American Pathologists 1, 2
Serum ferritin and transferrin saturation are essential to evaluate iron status, as iron deficiency can coexist with erythrocytosis, according to the American Society of Hematology 1
Peripheral blood smear review by a qualified hematologist is essential to identify abnormal morphology and assess for left shift, as stated by the International Society for Laboratory Hematology 1, 2

Hemoglobin >20 g/dL and hematocrit >65% with symptoms of hyperviscosity (headache, visual disturbances, dizziness) requires urgent therapeutic phlebotomy after excluding dehydration, as recommended by the National Institutes of Health 1
Elevated total band count (>1500 cells/mm³) has the highest likelihood ratio (14.5) for detecting bacterial infection, even without fever, as reported by the Infectious Diseases Society of America 2

Do not assume dehydration without confirming with clinical assessment, as a near-normal hemoglobin value may actually suggest dehydration masking anemia, as warned by the American Society of Nephrology 3, 4
Do not overlook the possibility of coexisting iron deficiency in patients with erythrocytosis, as iron-deficient red blood cells have reduced oxygen-carrying capacity and deformability, increasing stroke risk, as stated by the American Heart Association 1

Positive JAK2 mutation requires immediate hematology referral for management of polycythemia vera, as recommended by the National Comprehensive Cancer Network 1
Hemoglobin >20 g/dL with symptoms of hyperviscosity requires urgent hematology consultation, as stated by the American Society of Hematology 1
Unexplained splenomegaly with elevated blood counts mandates hematology evaluation, as recommended by the European Society of Medical Oncology 1