The possible value of platelet aggregation studies in patients with increased platelet number.

ADP, adrenalin and collagen platelet aggregation studies were performed in 54 patients with elevated platelet counts: 38 patients showed primary thrombocythemia and 16 secondary thrombocytosis. Patients with primary thrombocythemia (78.7%) showed a decrease aggregation pattern while in patients with secondary thrombocytosis platelet aggregation response was entirely normal. An increase in platelet aggregation was obtained in four patients with primary thrombocythemia. The platelet aggregation response did not appear to be related to circulating platelet number. A relationship between increased platelet aggregation and the occurrence of thrombosis was demonstrated. Similarly, a correction between impaired platelet aggregation and bleeding was also present. These results emphasize the diagnostic value of platelet aggregation studies in patients with elevated platelet number.