What initial screening value supports polycythemia vera?

• A. Hematocrit above 40%
• B. Hemoglobin above 16 g/dL
• C. Hematocrit above 48%
• D. Platelet count above 450,000/µL

Answer: (C)

Polycythemia vera causes an actual increase in red blood cell mass, so the earliest clue is a high hematocrit that reflects that excess red cells. A hematocrit in the high 40s is the screening threshold clinicians use to prompt further PV evaluation. In practice, this is about >49% in men and >48% in women, with some exam materials using 48% as a single cut-off. If the hematocrit is elevated this way, we pursue confirmatory steps such as JAK2 mutation testing and more precise RBC mass assessment.

Hemoglobin can rise in PV but is less specific because Hb levels can be influenced by hydration status and sex differences; platelet elevation is common but not specific to PV and can occur in many conditions. Thus, the hematocrit threshold best identifies the abnormal red cell mass that defines PV and triggers the diagnostic workup.