Special characteristics of morphology of platelets in patients with pheochromocytoma

Shape of platelets and ADP-induced platelet aggregation were studied in hyp ertensive patients with and without pheochromocytoma. In patients with pheo chromocytoma more than 17% of platelets had elongated bipolar shape with di minished aggregatory capacity. In patients with hypertension without pheoch romocytoma fraction of bipolar platelets was 7.7% or less and in healthy pe rsons it did not exceed 2.9%. After removal of the tumor number of bipolar platelets decreased. Same tendency was observed after administration of pra zosin while clonidine, nifedipine, captopril and atenolol did not influence the platelet formula. Thus fraction of bipolar platelets exceeding 17% is characteristic of pheochromocytoma and determination of platelet shape can be used as diagnostic test. Prazosin should be temporary stopped before thi s test.