In Vitro Detection of Platelet Antibody in Patients with Idiopathic Thrombocytopenic Purpura and Systemic Lupus Erythematosus

Abstract

Abstract Two technics have been developed, which make possible the in vitro detection of platelet antibody in patients with idiopathic thrombocytopenic purpura (ITP), and systemic lupus erythematosus (SLE). The dextran-platelet agglutination technic takes advantage of the enhancement of platelet agglutination in the presence of dextran which brings about a threefold increase in simple agglutination. The Platelet-Factor-3 test measures the ability of platelet antibody to injure platelets and in so doing, make Platelet Factor 3 available to the coagulation cascade, thus accelerating the fibrin clotting time. This technic, when compared to the simple platelet agglutination test, increases the detection sensitivity of antiplatelet factor(s) twenty-fivefold. The antiplatelet factor(s) as measured by these technics was found to be an immunoglobulin of the IgG class. The antiplatelet factor(s) was present in the sera of 85 per cent of patients with ITP and 88 per cent of patients with SLE. This antiplatelet factor(s) was absent in 25 consecutive healthy controls and in 22 out of 26 patients with thrombocytopenia not due to ITP or SLE. Although 88 per cent of patients with SLE had demonstrable antiplatelet activity in their serum only 2 out of 33 were thrombocytopenic. These observations suggested that a compensated thrombocytolytic state was present in these patients. This conclusion was consistent with the good correlation between an elevated large platelet index and the presence of antiplatelet factor in these patients.