Evaluation of the clinical utility of platelet aggregation studies

To determine the diagnostic importance of platelet aggregation studies, we evaluated the clinical utility of these assays by a retrospective review of 188 adult patients initially studied for bleeding abnormalities with platelet aggregation tests at a tertiary care hospital from 1984 to 1987. The primary indications for requesting the tests in our patient population were for the evaluation of a positive bleeding history or abnormal bleeding time (68%), hypercoagulability (17%), thrombocytosis (9%), or a family history of a bleeding disorder (6%). There was a statistically higher incidence of platelet aggregation test abnormalities in patients with highly abnormal bleeding times (40%), in patients with thrombocytosis from myeloproliferative disorders (65%), and in patients with a family history of a bleeding disorder (58%), compared to the other groups studied (16-29%). Of the 64 platelet aggregation tests performed that were abnormal, the following abnormalities were identified: 19 aspirin-like defects (poor response to arachidonate and decreased second wave responses to weak agonists), which were presumably drug-induced, ten myeloproliferative-type disorder defects (abnormal response to epinephrine predominantly) in patients known to have myeloproliferative disease, 34 abnormal patterns not characterized as aspirin or myeloproliferative disorder related, four of which ultimately led to a diagnosis of storage pool disease, and one spontaneous aggregation defect. Our results suggest that platelet aggregation tests rarely lead to the diagnosis of a specific, previously undiagnosed platelet function disorder. Specific recommendations are given for efficient utilization of platelet aggregation tests.