The assessment of drug-dependent and isoimmune antiplatelet antibodies by the use of platelet aggregometry.

The technique of platelet aggregometry provides a simple, quantitative, and specific method for the detection of drug-dependent and isoimmune antiplatelet antibodies. In the presence of antiquinidine antibody, quinidine causes lysis of normal platelets in platelet-rich plasma. The resulting changes in optical density are readily detected in the aggregometer. The initial rate of lysis is a function of the antibody titer, but is relatively independent of the platelet count. In vitro, quinidine produces platelet swelling and inhibits aggregation of platelets by adenosine diphosphate, epinephrine, and collagen. Isoimmune antibodies cause aggregation of platelets in platelet-rich plasma. In studies of a single family the rate of aggregation is proportional to the number of HL-A antigens present on the normal platelets against which the antibody is directed. The simple technique of platelet aggregometry may be a useful adjunct in the selection of compatible donors for platelet transfusion. Serum derived from patients with idiopathic thromboytopenic purpura did not cause platelet aggregation.