Diagnostic and differential criteria of essential thrombocythemia and reactive thrombocytosis.

Among the chronic myeloproliferative disorders essential thrombocythemia (ET) is known to be a distinct clinical entity in which an excessive number of morphologically and functionally abnormal platelets are produced. The clonal nature of the disease is well established. Based on a review of the literature the present authors propose the following novel criteria for the diagnosis of ET: A1. Platelet count in excess of 600 x 10(9)/L. A2. No increase in red-cell mass (RCM) in the presence of stainable iron in the bone marrow or failure of iron trial (RCM < 36 mL/kg in males and < 32 mL/kg in females; or RCM < 25% above mean normal predicted value*). A3. No Philadelphia chromosome. A4. Megakaryocytic hyperplasia (= increased megakaryocyte number and size) in histological sections of bone marrow and/or increased megakaryocytic ploidy (two-color flow cytometry); no collagen fibrosis. B1. Splenomegaly on isotopic scan or echogram. B2. Unstimulated growth of BFU-E and/or CFU-Meg present. B3. Normal ESR/fibrinogen. The diagnosis of ET is considered to be established if A1 + A2 + A3 + A4 or A1 + A2 + A3 + two B-criteria are fulfilled. (* Br J Haematol 1995; 89:748-756.)