Detection of platelet antibodies in chronic idiopathic thrombocytopenic purpura (ITP). A comparative study using flow cytometry, a whole platelet ELISA, and an antigen capture ELISA.

Chronic idiopathic thrombocytopenic purpura (ITP) is a consequence of rapid platelet destruction caused by circulating platelet antibodies. In this study we compared three methods for detecting serum platelet antibodies in a population of 65 patients with chronic ITP. In two of the techniques intact platelets were used as the antibody target, i.e. the whole platelet ELISA and the flow cytometric assay; in the third an antigen-specific modified antigen capture ELISA (MACE) was employed. By using the whole platelet ELISA and the flow cytometric assay 35% and 45% of the patients, respectively, displayed an antiplatelet antibody. In most cases (26 or 29 patients) IgG was the predominant antiplatelet immunoglobulin. As analysed using the MACE-technique glycoprotein (GP) Ib/IX-specific antibodies occurred with the same frequency as antibodies specific for GPIIb/IIIa. Moreover, there was a poor correlation between the MACE results on the one hand and results from the intact platelet-based techniques on the other, i.e. several patients were positive in one assay whereas they were negative in the other. We conclude that all three techniques have their merits and demerits; it appears reasonable that they should be used together in the evaluation of the autoimmune process of chronic ITP.