A radioimmunoassay for erythropoietin.

We describe the development of a radioimmunoassay (RIA) for erythropoietin. Antisera were raised in rabbits with an impure human urinary erythropoietin preparation used as immunogen, but with pure human erytropoietin serving as the labeled antigen in the RIA and as a primary standard. The immunoreactivity of erythropoietin is not altered significantly by the mode of labeling with radioiodine, even though the biologic activity is lost. With this method, it is possible to detect 2--3 mU of erythropoietin in a volume of 0.1--0.3 ml. Therefore, the method can be used for detection of normal and subnormal serum titers as well as elevated titers. RIA for erythropoietin does not distinguish between the native (active in vivo) and the asialo form (inactive in vivo) and cannot yet be used for routine monitoring of crude fractions during purification.