RELIABILITY OF AUTOMATED PLATELET COUNTS - COMPARISON WITH MANUAL METHOD AND UTILITY FOR PREDICTION OF CLINICAL BLEEDING

The 20 x 10(9)/L (20,000/mu l) threshold for prophylactic platelet tra nsfusion may be unnecessarily high. The widespread use of this thresho ld may reflect lack of confidence in the reliability of low platelet c ounts. We evaluated the performance of automated platelet counts and t heir relation to clinical bleeding. First, we prepared serial blood di lutions with ''target'' platelet counts from 2 to 40 x 10(9)/L. For th e 48 measurements on 2 x 10(9)/L ''target'' dilutions, values of 1 or 2 x 10(9)/L were obtained with the Sysmex NE-8000 analyzer (mean 1.44 x 10(9)/L; SD 0.31 x 10(9)/L). Similarly, for 5 x 10(9)/L ''target'' c ounts, automated counts were 3-6 x 10(9)/L(mean 4.42 x 10(9)/L; SD 0.1 8 x 10(9)/L). Similar results were observed with all other ''target'' levels, with coefficients of variation (CV) from 6.39% to 7.71% with 1 0-40 x 10(9)/L ''target'' values. Secondly, we compared triplicate aut omated and manual platelet counts on thrombocytopenic patients with pl atelet counts from 4-30 x 10(9)/L. The triplicate automated platelet c ounts differed by no more than 5 x 10(9)/L among themselves, whereas t he manual counts varied by as much as 30 x 10(9)/L. Mean platelet coun ts: automated, 14.40 x 10(9)/L(CV 10.12%); manual, 16.48 x 10(9)/L(CV 30.39%) (P = 0.038 for counts; P < 0.001 for CV). Finally, we prospect ively evaluated bleeding in thrombocytopenic patients (1,809 patient-d ays of observation). Univariate and multivariate logistic regression a nalysis revealed highly significant correlations between the automated platelet count and major and minor bleeding manifestations. Thus, aut omated platelet counts are highly reliable and accurately predict clin ical bleeding. The use of automated analyzers should facilitate improv ed prophylactic platelet transfusion protocols. (C) 1995 Wiley-Liss, I nc.