A rapid method for assessing megathrombocytes: its application to thrombocytotic and acquired thrombocytopenic states.

A rapid technique suitable for routine laboratory use for determining the percentage of large platelets in the peripheral blood is described. In 50 haematologically normal subjects, megathrombocytes (platelets with a volume of 16-33 fl) constituted 3.0-16.6% (mean +/- 2 SD) of the platelet count. Of the 10 patients examined with immune thrombocytopenic purpura, an increased percentage of megathrombocytes (mean 26.6%) was found in all with severe thrombocytopenia, and in 6 of 8 (mean 19.8%) with moderate thrombocytopenia; the percentages were not influenced by prior splenectomy. Six of 12 patients with severe hypomegakaryocytic thrombocytopenia had an increased percentage of large platelets (mean 15.9%), as did one of 21 patients (mean 9.9%) with moderate thrombocytopenia of simimlar aetiology. When patients with nearly identical platelet counts were compared, the mean percentage of megathrombocytes was greater in immune than in hypomegakaryocytic thrombocytopenia for both severe (t=3.17, P less than 0.01) and moderate (t=4.5, P less than 0.001) thrombocytopenia. An increased percentage of large platelets (mean 21.9%) was found in 6 to 8 patients with disseminated intravascular coagulation, in 7 of 20 (mean 15.8%) with chronic myeloproliferative disorders and in one of 15 (mean 8.8%) with reactive thrombocytosis. Determination of the percentage of megathrombocytes by this technique assists in differentiating immune thrombocytopenia from hypomegakaryocytic thrombocytopenia, in diagnosing mild disseminated intravascular coagulation, and in determining whether thrombocytosis is reactive or a consequence of a myeloproliferative disorders.