Detection of platelet-bound and serum antibodies in autoimmune thrombocytopenia by enzyme-linked assay.

Platelet antibodies were looked for in 47 patients with autoimmune thrombocytopenia using a modification of the enzyme-linked assay previously described. Surface-bound antibodies measured as increased platelet-associated IgG were found in 32 (68%) of the patients. After incubation in test sera, the platelet-associated IgG of normal donor platelets was significantly increased in 27 of the 47 patients (57%), thus demonstrating the presence of platelet antibodies free in their sera. 6 patients had antibodies only in the serum without any elevation of their platelet-associated IgG. When both tests are evaluated together no antibody was detected by either the direct or the indirect test in 9 of the 47 patients (29%) studied. The technique used is described and the interpretation of our results discussed.