Anti-platelet antibody determination by platelet factor 3 assay.

Anti-platelet antibody determinations by a recently introduced platelet factor 3 assay (Pf-3 assay) were evaluated in 159 specimens from 95 patients who had low platelet counts. As a standard procedure, the 51Cr lysis test (51Cr test) was used. The 51Cr test and Pf-3 assay had an excellent correlation (results agreed for 80.5% of 159 specimens tested). Overall positive results for the 159 specimens were 27.7% by the 51Cr test and 22.0% by the Pf-3 assay. A significantly high incidence of anti-platelet antibodies (71.4%) was found in patients who had received more than 10 units of blood transfusions, in contrast to a non-transfused group, which had an incidence of 6.3%. The difference between transfused and non-transfused groups was significant (x2 = 11.854, p less than 0.001). The Pf-3 assay is easy to perform in most laboratories and yet sensitive enough to detect anti-platelet antibodies that were detectable by the 51Cr test.