The assessment of red cell survival in normal subjects and in patients with haemolytic disorders and ineffective erythropoiesis using the radioiron occupancy method.

A direct method for measuring red cell lifespan in vivo using the radioiron occupancy method (Dagg et al, 1972) has been applied to eight normal subjects. The mean red cell lifespan was 116 d with a range of 104-124 d. To establish the method clinically in the presence of haemolysis and ineffective erythropoiesis, 22 patients with haemolytic disease and six patients with megaloblastic and sideroblastic anaemia were studied. All 22 patients with haemolytic anaemia had shortening of the red cell lifespan, with a range from 62 to 10 d; the results were compared with red cell lifespan derived from simultaneous radiochromium studies (Bentley et al, 1974). A close agreement between the two methods was obtained (r = 0.87; P less than 0.001). To assess the validity of the method in the presence of ineffective erythropoiesis, double isotope studies were also carried out in three patients with megaloblastic anaemia and three with sideroblastic anaemia. Close agreement was again obtained between lifespan measurements obtained from radioiron occupancy data and those derived from radiochromium studies, suggesting that the presence of significant ineffective erythropoiesis does not invalidate the method. The theoretical considerations involved in the application of the radioiron occupancy method to haemolytic states are discussed.