| Summary: | Objective: To identify antiplatelet antibodies by flow cytometry (direct method) in patients with thrombocytopenia. Methods: BetweenJanuary 1997 and March 2004 a total of 15100 patients were referred tothe Centro de Hematologia de São Paulo for hematological investigationof several diagnoses (anemia, leukopenia, thrombocytopenia,coagulation abnormalities, adenomegaly, leukemia and others). Ofthose, 1057 were referred because of thrombocytopenia and weredivided into two groups: Group Idiopathic thrombocytopenic purpura,with no identifiable cause; and Group Other thrombocytopenia, whichincluded low normal platelet counts cause to be established, hepatitisC and HIV infection, hypersplenism, EDTA-induced artifacts, laboratoryerror, and other causes. Flow cytometry immunophenotyping wasdone in 115 cases to identify platelet autoantibodies (direct method).Results: Of the total number of patients, 1057 (7%) presented lowplatelet counts, 670 were females (63.4%) and age range of one to75 years. Of the 115 cases (9.7%) submitted to immunophenotyping,the results were positive in 40% and the test was inconclusive in 5%.Idiopathic thrombocytopenic purpura was found in 52% of patients,more often in women. Hepatitis C virus infection was found in 7%and HIV infection in 1%. Low normal platelet counts were foundin 17%, laboratory errors in 6%, and laboratory artifacts in 1% ofcases. Platelet autoantibodies were found in 76.9% of all idiopathicthrombocytopenic purpura cases. It was negative in 83.3% of the lownormal counts. Conclusion: antiplatelet autoantibodies when presenthelp to diagnose idiopathic thrombocytopenic purpura. When absent,suggest other causes of thrombocytopenia.
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