Platelet peroxidase of circulating thrombocytes in acquired refractory anaemias.

The platelet peroxidase (PPO) content of circulating thrombocytes was determined in 10 healthy controls and in 18 cases of acquired refractory anaemia (2 with refractory anaemia, 4 with sideroblastic refractory anaemia, 8 with refractory anaemia with excess of blasts, 3 with refractory anaemia in transformation and 1 with chronic myelomonocytic leukaemia). The thrombocytes of the controls were invariably PPO-positive. No peroxidase deficiency was found in the 4 patients with sideroblastic refractory anaemia. Of the remaining 14 cases PPO-positive and PPO-negative thrombocytes coexisted in 8. Only in 1 case of refractory anaemia with excess of blasts were circulating platelet peroxidase-positive micromegakaryocytes demonstrated. PPO deficiency seems to be an important dysthrombopoietic feature detectable only at an ultrastructural level.