MEAN PLATELET VOLUME IMPROVES UPON THE MEGATHROMBOCYTE INDEX BUT CANNOT REPLACE THE BLOOD FILM EXAMINATION IN THE EVALUATION OF THROMBOCYTOPENIA

The measurement of the number of platelets larger than 3 microns (megathrombocyte index) is the first element in the evaluation of thrombocytopenia. This is currently performed by counting the number of large platelets on the peripheral blood film. The MPV (mean platelet volume) is an automated measurement of the platelet volume. This study examines the mean values, correlations, sensitivity, specificity and the receiver operating characteristic curve (comparison of two tests) to determine which of these tests better separates the production state. For increased vs. decreased production, the MPV was 10.0 + 1.9 fL and 8.0 + 1.5 fL (P < .0001) respectively and the megathrombocyte index (MEGA) was 19.0 + 17.6% and 11.5 + 14.9% (P < .007) respectively. The correlation with the state of production was better for MPV (R = .47) than for MEGA (R = .20). For the MPV a sensitivity of 80% occurred with the MPV greater-than-or-equal-to 8.4 fL with a specificity of 71%. For a MEGA greater-than-or-equal-to 6%, the sensitivity was 80% but the specificity was 43%. For any MPV the sensitivity and specificity were better than for any MEGA. The Receiver Operating Characteristic Curve demonstrated that the MPV is a better test than the MEGA for separating the production into increased and decreased states. The MPV is a better test than the MEGA and will add to, but not replace, examination of the peripheral blood film in the diagnosis of thrombocytopenia. (C) 1993 Wiley-Liss, Inc.