SCREENING FOR PLATELET AUTOANTIBODIES BY FLOW-CYTOMETRY AND THEIR EVALUATION BY THE MAIPA TECHNIQUE

The determination of platelet antibodies assists in the diagnosis of i mmune thrombocytopenia. Among the Various techniques which have been u sed two major ways for the determination of these antibodies have ente red the routine use, determination of in vivo platelet bound total IgG , termed platelet-associated IgG, PAIgG, and that of specifically to p articular platelet glycoproteins bound IgG, GP-IgG. The former has bee n found to be non-specific, and the evaluation of the latter is rather laborious. Furthermore, both require a large number of platelets. By flowcytometry, however, PAIgG can be determined even if platelet count s are very low. We therefore evaluated in 30 patients' samples if the flowcytometric determination of PAIgG can serve to screen for platelet antibodies. Positive samples subsequently are evaluated by a glycopro tein-specific detection technique (MAIPA). We show that in patients wi th suspected autoimmune thrombocytopenia (AITP) and in secondary AITP PAIgG is elevated in 83%. However, only 30% of patients' samples have detectable antibodies by the MAIPA technique. Based on the findings th at by the MA[PA technique antibodies were only detectable in samples w hich had also elevated levels of PAIgG we consider the flowcytometric determination of PAIgG useful for screening, prior to the more laborio us investigation by the MAIPA assay.