Detection of Antiplatelet Antibody With a Platelet Immunofluorescence Assay

An indirect platelet immunofluorescence assay (PIFA) was developed for detection of circulating antiplatelet antibody in dogs with suspected immune‐mediated thrombocytopenia (ITP). The PIFA was performed on 10 healthy dogs with normal platelet counts; 76 thrombocytopenic dogs, 20 of which were suspected of having ITP; and 18 dogs with other diseases and normal platelet counts. All normal dogs had negative test results. Fourteen (70%) of 20 dogs suspected of having ITP had positive test results. Fifteen of the remaining 56 thrombocytopenic dogs had positive test results, 9 had cancer and 6 had other immune‐mediated diseases including systemic lupus erythematosus (SLE). In this study, the PIFA assay seemed to be more sensitive (70%) than the megakaryocyte immunofluorescence assay (41 %) in the diagnosis of ITP. Of the 9 PIFA‐positive dogs with neoplasia, 6 had lymphoproliferative disorders. The PI FA was positive in 5 of 18 diseased dogs with normal platelet counts. There was an inverse relationship between the platelet count and the intensity of fluorescence in the PIFA‐positive dogs. We conclude that the PIFA is a sensitive screening method for detecting circulating antiplatelet antibody.