Detection of platelet antibodies by flow cytometric analysis

A rapid, sensitive indirect immunofluorescence assay utilizing flow cytometry to detect immune-mediated thrombocytopenia is described. Fluorescein-conjugated F(ab')2 antihuman IgG or IgGAM is reacted with donor platelets after their incubation with test sera and the resulting immune complex is measured using flow cytometric analysis. With this technique excess of Ig on the platelet, expressed as a ratio of fluorescence of test sera/autologous control sera, was noted in 24 of 30 patients (80%) with immune thrombocytopenias caused by auto- or allo-antiplatelet antibodies. Twenty-four sera from nonimmune thrombocytopenic patients were consistently negative. This technique has the advantage of being highly reproducible and avoids the subjective interpretation inherent with manual immunofluorescence assays.