What is the hemoglobin (Hb) cutoff for diagnosing polycythemia in a patient with a history of deep vein thrombosis (DVT)?

Hemoglobin Cutoff for Diagnosing Polycythemia Vera

The hemoglobin cutoff for diagnosing polycythemia vera is ≥18.5 g/dL in men and ≥16.5 g/dL in women, according to the revised WHO diagnostic criteria. 1

Standard Diagnostic Thresholds

The WHO diagnostic criteria establish clear hemoglobin thresholds as part of the first major criterion for polycythemia vera (PV): 1

• Men: Hemoglobin ≥18.5 g/dL or hematocrit ≥49%
• Women: Hemoglobin ≥16.5 g/dL or hematocrit ≥48%

These values represent the 99th percentile of method-specific reference ranges adjusted for age, sex, and altitude of residence. 1

Special Consideration for DVT Patients

In patients with a history of deep vein thrombosis, the same hemoglobin cutoffs apply, but the diagnostic threshold for suspicion should be lower. 1 The Mayo Clinic guidelines specifically identify unusual thrombosis (including DVT) as a PV-related feature that warrants investigation even when hemoglobin/hematocrit values are borderline-high or within the upper-normal range. 1

For DVT patients, pursue PV workup if any of the following are present: 1

• Hemoglobin/hematocrit above the 95th percentile for sex and race
• Documented sustained increase of ≥2 g/dL hemoglobin from baseline, regardless of whether values remain within normal reference ranges 1, 2
• Borderline-high hematocrit accompanied by other PV-related features (thrombocytosis, leukocytosis, microcytosis from iron deficiency, splenomegaly, aquagenic pruritus, or erythromelalgia) 1

Critical Pitfalls in DVT Patients

Iron deficiency can mask true polycythemia and must be excluded before dismissing the diagnosis. 1 In routine clinical practice, you should not be prevented from making a working diagnosis of PV in the presence of iron deficiency, even if WHO hemoglobin criteria are not met. 1 However, for formal diagnosis in research or clinical trials, iron replacement is required to demonstrate meeting WHO criteria. 1

Dehydration is the most common cause of falsely elevated hematocrit and must be verified before proceeding with full workup. 3 This is particularly relevant in DVT patients who may have reduced mobility or fluid intake.

Diagnostic Algorithm for DVT Patients

When PV is suspected in a DVT patient: 1, 2

1. Measure serum erythropoietin (EPO): Low EPO has >90% specificity for PV, though normal EPO does not exclude it (sensitivity <70%). 1, 3 PV is unlikely with elevated EPO. 1

2. Order JAK2 mutation testing: JAK2 V617F (exon 14) is present in >95% of PV cases. 2, 3 If negative, proceed to JAK2 exon 12 testing, which captures the remaining ~3% of cases. 2, 3

3. Bone marrow biopsy: Shows hypercellularity with trilineage growth (panmyelosis) in PV. 1, 3 This is particularly important when JAK2 is negative or diagnosis remains uncertain. 1

Hematocrit as Alternative Measurement

Hematocrit shows better diagnostic accuracy than hemoglobin for identifying true polycythemia. 4 The optimal hematocrit values to indicate need for red cell mass study are: 4

• Men: 0.50 L/L (50%) with specificity 75% and sensitivity 87.5%
• Women: 0.48 L/L (48%) with specificity 73% and sensitivity 94%

Lowering the male threshold to 0.48 L/L increases sensitivity to 95%. 4 Male patients with hematocrit >60% and female patients with hematocrit >55% always have absolute polycythemia and do not require red cell mass measurement. 5

Management Implications for DVT Patients

Once PV is diagnosed in a DVT patient, immediate therapeutic intervention is critical to prevent recurrent thrombosis. 6, 7 All patients require: 6, 7

• Therapeutic phlebotomy to maintain hematocrit <45% (significantly reduces thrombotic risk)
• Low-dose aspirin 100 mg daily unless contraindicated

Patients with prior thrombosis are automatically classified as high-risk and require cytoreductive therapy (hydroxyurea, interferon alfa, or pegylated interferon) in addition to phlebotomy and aspirin. 6, 7