Biological Assay of Human Urinary Erythropoietic Stimulating Factor (ESF)

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Abstract
The concentration of erythropoietic stimulating factor (ESF) in the urine of thalassemia patients increases with the severity of the anemia. Subjects with hemoglobin levels below 4 g% may reasonably be expected to provide urine with a high titer of human ESF. A biological assay depending upon the single unit obtained by the additive changes in hematocrit and reticulocyte values of rats has been developed which produces a cheaper and more reliable method of screening samples for ESF activity than the starved rat red cell Fe59 uptake procedure. The latter method, however, is more sensitive and therefore more useful in following the purification of ESF preparations of established potency.