Screening for platelet auto-antibodies by flow cytometry and their evaluation by the MAIPA technique.

The determination of platelet antibodies assists in the diagnosis of immune thrombocytopenia. Among the various techniques which have been used two major ways for the determination of these antibodies have entered the routine use, determination of in vivo platelet bound total IgG, termed platelet-associated IgG, PAIgG, and that of specifically to particular platelet glycoproteins bound IgG, GP-IgG. The former has been 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 counts 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 glycoprotein-specific detection technique (MAIPA). We show that in patients with 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 that by the MAIPA technique antibodies were only detectable in samples which had also elevated levels of PAIgG we consider the flowcytometric determination of PAIgG useful for screening, prior to the more laborious investigation by the MAIPA assay.