Increased Erythrocyte Count on Top of Bone Marrow Histology but not Serum EPO Level or JAK2 Mutation Load Discriminates between JAK2V617F Mutated Essential Thrombocythemia and Polycythemia Vera

Bone marrow histology is a powerful tool to differentiate between the myeloproliferative neoplasms (MPN) of essential thrombocythemia (ET) and polycythemia vera (PV) from all variants of primary or secondary erythrocytosis and reactive thrombocytosis with a sensitivity and specificity of 100%. Bone marrow histopathology on its own is not reliable to differentiate between WHO defined ET and PV. The majority of JAK2 mutated ET and all PV patients have increased scores for the leukocyte alkaline phosphatase (LAP) stain. The morphology of large pleomorphic megakarocytes were not different in JAK2 mutated ET, prodromal PV, and overt PV. Serum EPO level or JAK2 allele mutation load do not discriminate between ET and prodromal PV versus classical and masked PV in JAK2V617F positive trilinear MPN. A typical MPN bone marrow histology, erythrocytes above 5.8 × 1012/L in males and 5.6 × 1012/l in females (normal cut-off value is 5.5 × 1012/L in females) separates overt and masked PV from ET and prodromal PV obviating the need of RCM measurement.