Typical Hemoglobin and Hematocrit Levels in Polycythemia Vera
In polycythemia vera (PV), diagnostic hemoglobin thresholds are ≥18.5 g/dL in men and ≥16.5 g/dL in women, with corresponding hematocrit values typically >52% in men and >48% in women. 1, 2
Diagnostic Criteria for Polycythemia Vera
According to the World Health Organization (WHO) criteria, the diagnosis of PV requires specific hemoglobin/hematocrit thresholds:
Major Criteria:
Elevated red blood cell parameters:
- Hemoglobin ≥18.5 g/dL in men, ≥16.5 g/dL in women, OR
- Hematocrit >99th percentile of reference range for age, sex, and altitude, OR
- Hemoglobin >17 g/dL in men, >15 g/dL in women with documented sustained increase of ≥2 g/dL from baseline, OR
- Elevated red cell mass >25% above mean normal predicted value
Presence of JAK2V617F or JAK2 exon 12 mutation
Minor Criteria:
- Bone marrow biopsy showing hypercellularity with trilineage growth
- Serum erythropoietin level below reference range
- Endogenous erythroid colony formation in vitro
Diagnosis requires either both major criteria plus one minor criterion, or the first major criterion plus two minor criteria 1.
Clinical Considerations
Masked Polycythemia Vera
It's important to note that some patients may have "masked PV" with normal or near-normal hemoglobin/hematocrit levels:
- These patients may present with hemoglobin <18.5 g/dL in men (range 16.0-18.4) and <16.5 g/dL in women (range 15.0-16.4) 3
- Masked PV can still be diagnosed through JAK2 mutation testing and bone marrow examination
- These patients often have higher platelet counts and increased bone marrow reticulin fibrosis 3
Factors Affecting Hemoglobin/Hematocrit Levels
Several factors can influence hemoglobin/hematocrit values in PV patients:
- Iron deficiency: Common in PV and can mask true hemoglobin/hematocrit levels
- Blood loss: May temporarily normalize hemoglobin/hematocrit
- Plasma volume expansion: Can dilute red cell concentration
Diagnostic Accuracy
- Hematocrit shows better diagnostic accuracy than hemoglobin for PV 4
- The best threshold values for hematocrit to indicate the need for red cell mass study are:
- 0.50 L/L (50%) in males (specificity 75%, sensitivity 87.5%)
- 0.48 L/L (48%) in females (specificity 73%, sensitivity 94%) 4
Management Implications
The target hematocrit for PV management is <45% through therapeutic phlebotomy, regardless of initial presentation values 2, 5. This target is associated with reduced thrombotic risk, which is a major cause of morbidity and mortality in PV patients.
Common Pitfalls
- Overlooking masked PV in patients with normal hemoglobin/hematocrit
- Failing to investigate for PV in patients with unusual site thrombosis (e.g., splanchnic veins) even with normal blood counts 6
- Not considering iron deficiency as a cause of "normal" hemoglobin/hematocrit in a patient with PV
In patients with suspected PV but normal hemoglobin/hematocrit, JAK2 mutation testing and bone marrow examination are essential for accurate diagnosis 6.