What is the threshold hematocrit (Hct) level to diagnose polycythemia in a male?

Diagnostic Threshold for Polycythemia in Males

For males, polycythemia vera (PV) is diagnosed when the hematocrit is greater than 52% or hemoglobin is greater than or equal to 18.5 g/dL, according to the World Health Organization (WHO) criteria. 1

Primary Diagnostic Criteria

The diagnosis of polycythemia vera in males relies on the following thresholds:

• Hemoglobin ≥ 18.5 g/dL OR hematocrit greater than the 99th percentile of method-specific reference range for age, sex, and altitude of residence 1
• Alternatively, a hematocrit > 52% in males with JAK2 mutation (per British Committee for Standards in Haematology guidelines) 2
• An elevated red cell mass > 25% above mean normal predicted value can also be used as diagnostic evidence 1

Additional Diagnostic Considerations

When evaluating a patient with suspected polycythemia, several important factors should be considered:

• Males with hematocrit > 60% always have absolute polycythemia and do not require additional blood volume studies 3
• Early or masked PV may present with hemoglobin levels between 16.0-18.4 g/dL in males, particularly when accompanied by other features suggestive of PV 2
• A documented and sustained increase in hemoglobin of at least 2 g/dL from baseline (not attributable to iron deficiency correction) may indicate PV even if absolute thresholds aren't met 1

Diagnostic Algorithm

1. If hematocrit > 60% in males, absolute polycythemia is confirmed 3
2. If hematocrit is 52-60% or hemoglobin ≥ 18.5 g/dL, proceed with JAK2 mutation testing 1
3. If hematocrit/hemoglobin is below these thresholds but there is clinical suspicion:
   • Check for JAK2 mutation (present in >95% of PV cases) 4
   • Measure serum erythropoietin level (typically low in PV) 1, 5
   • Consider bone marrow biopsy showing hypercellularity with trilineage growth 1

Common Pitfalls and Caveats

• Iron deficiency may mask true polycythemia by lowering hemoglobin/hematocrit levels; consider iron replacement before excluding PV 1
• Smoking is the most frequent cause of increased hematocrit and should be addressed before ordering blood volume studies 3
• Recent WHO criteria updates (2016) have lowered the hemoglobin threshold to 16.5 g/dL in males, allowing earlier diagnosis of PV 6
• Patients with masked PV (hemoglobin below traditional thresholds) may have worse survival outcomes compared to those with overt PV 2
• The presence of splenomegaly, elevated white blood cell count, or thrombocytosis alongside increased hematocrit strongly suggests PV 3