In PV, which cell lines are increased?

• A. All three myeloid lineages, primarily RBCs
• B. Red cells only
• C. Lymphocytes
• D. Platelets only

Answer: (A)

Polycythemia vera is a myeloproliferative neoplasm driven by a JAK2 mutation that causes clonal expansion of hematopoietic cells across the myeloid lineages. This means there is an overall increase in red blood cells, white blood cells, and platelets — a phenomenon often described as panmyeloproliferation. The red cell mass is typically the most markedly increased, leading to elevated hematocrit and hyperviscosity, but white cells and platelets are also elevated. That’s why the correct statement is that all three myeloid lineages are increased, with red cells usually dominating. Notably, it’s not limited to red cells, nor restricted to lymphocytes or platelets alone.