What are the laboratory tests for polycythemia (excessive red blood cell count)?

From the Guidelines

Laboratory tests for polycythemia should include a complete blood count (CBC) with hemoglobin and hematocrit, erythropoietin (EPO) levels, JAK2 V617F mutation analysis, and bone marrow biopsy to distinguish between primary polycythemia vera and secondary causes, as recommended by the most recent guidelines 1.

Key Diagnostic Findings

• Elevated hemoglobin (>16.5 g/dL in men, >16.0 g/dL in women) and hematocrit (>49% in men, >48% in women) are key diagnostic findings.
• Low serum EPO levels are highly suggestive but not diagnostic of polycythemia vera (PV), with a specificity of >90% 1.

Additional Testing

• Arterial blood gases may help identify hypoxia-induced polycythemia.
• Comprehensive metabolic panel, liver and kidney function tests should be performed to evaluate for underlying conditions.
• Serum ferritin and iron studies help assess iron stores.
• For suspected polycythemia vera, testing should follow WHO criteria, including JAK2 exon 12 mutations if JAK2 V617F is negative 1.
• Abdominal ultrasound may be ordered to check for splenomegaly.

Diagnostic Criteria

• The WHO criteria for polycythemia vera include two major criteria: laboratory evidence of increased hemoglobin, hematocrit, or red cell mass, and the presence of a JAK2 mutation 1.
• Minor criteria include MPD-consistent bone marrow histology, serum erythropoietin level below the reference range for normal, and presence of endogenous erythroid colonies 1.
• Diagnosis of PV requires either the presence of both major criteria and at least one minor criterion or the presence of the first major criterion and at least two minor criteria 1.

From the Research

Laboratory Tests for Polycythemia

• The complete blood count (CBC) is a crucial laboratory test for evaluating polycythemia, as it includes components such as red blood cell count, hemoglobin, hematocrit, and red blood cell indices 2, 3.
• An increased hematocrit can be caused by primary proliferative polycythemia, secondary polycythemia, relative polycythemia, or modifications of the red cell mass and plasma volume within their normal ranges 4.
• Blood volume studies may be necessary to diagnose polycythemia, especially in patients with an increased hematocrit and no other clinical or biological signs suggestive of any form of polycythemia 4.
• The associations of an increased hematocrit with splenomegaly, a raised white blood cell count, or thrombocytosis are indicators for primary proliferative polycythemia (PPP) 4.
• Male patients with a hematocrit over 60% and female patients with a hematocrit over 55% always have absolute polycythemia 4.

Diagnostic Approach

• The approach to diagnosis and classification of patients with polycythemia involves general and specific guidelines for the management of patients with polycythemia vera, secondary polycythemia, and relative polycythemia 5.
• Clinical data such as splenomegaly, aquagenic pruritus, and erythromelalgia often exist in PPP, whereas other symptoms such as dyspnea are more likely to be associated with secondary polycythemia 4.
• Smoking is the most frequent cause of an increased hematocrit, and smokers with an increased hematocrit may be asked to stop smoking before ordering blood volume studies 4.