THE RATE OF REMOVAL OF RADIOACTIVE IRON FROM THE PLASMA—AN INDEX OF ERYTHROPOIESIS 1

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Abstract
The rate of disappearance of radioactive iron from the plasma was studied in an attempt to elucidate one phase of Fe metabolism in anemic individuals. Labelled ferric beta-1-globulinate, prepared by incubating Fe59 chloride with plasma fraction IV-7, was injected intraven. in 8 normal subjects and in 32 persons with various blood disorders. The disappearance of the Fe59 from the circulating plasma was exponential in all cases. The rate of removal of Fe59 was markedly prolonged in patients with aplasia or hypo-plasia of the bone marrow, as compared to the normal. When there was increased marrow erythropoiesis, as occurs in polycythemia vera, hemolytic anemia and Fe deficiency anemia, there was an increased rate of removal of Fe59 from the plasma. Thus a correlation between erythropoiesis and the rate of disappearance of Fe59 from the plasma is established. Further confirmatory evidence of this hypothesis is afforded by the demonstration that in the syndrome of myelofibrosis where there is extra medullary erythropoiesis in the spleen X-radiation to this organ results in decreased red cell production and a concomitant prolongation of the rate of Fe disappearance from the plasma. In polycythemia vera, following therapy with which depresses erythropoiesis, the rapid disappearance rate returns to normal. On the basis of animal expts. of other investigators, it is possible that greater than normal Fe stores, as occurs in hemosiderosis, may prolong the plasma Fe59 turnover. It is concluded that with normal body Fe stores the plasma Fe59 disappearance rate is a sensitive measure of the integrity of the erythropoietic tissue of the body.