CHARACTERIZATION OF ANTIBODIES DIRECTED AGAINST PLATELET CRYPTANTIGENS DETECTED DURING THE IMMUNOLOGICAL STUDY OF 356 CONSECUTIVE PATIENTS WITH PRESUMED AUTOIMMUNE THROMBOCYTOPENIA (AITP)

Cryptic antigens are detected by antibodies present in a wide spectrum of patients with or without thrombocytopenia, and even in healthy ind ividuals. They are produced for unknown reasons and do not react with antigens of native platelets, but only with altered platelets. Cryptan tigen antibodies may not only result in spuriously low platelet counts , but also in 'falsely' positive tests for platelet antibodies. We rep ort our experience in the characterization of the different types of a ntibodies directed against cryptantigens of platelets: EDTA-dependent antibodies, PEA-dependent antibodies, EDTA-PFA-dependent antibodies an d cold agglutinins. These antibodies were detected in the course of th e serological study of 37 patients from a group of 356 (10%) whose blo od was sent to our laboratory for platelet antibody testing. Pseudothr ombocytopenia was diagnosed in 24 cases. Twenty-one of these showed ED TA-dependent or EDTA-PFA-dependent platelet agglutination and three we re due to the presence of cold agglutinins. In 13 patients the thrombo cytopenia was genuine. Eleven of these presented EDTA-dependent or EDT A-PFA-dependent antibodies in their serum and in the two remaining cas es PFA-dependent antibodies were found. Cryptantigen antibodies were a lso detected in 9 out of 228 (4%) blood donors who were used as health y controls in the platelet immunofluorescence test. In the light of th e results obtained we put forward some guidelines to detect the presen ce of these antibodies and establish an accurate serological and clini cal diagnosis of the autoimmune thrombocytopenias.