PLASMA ERYTHROPOIETIN IN POLYCYTHEMIA

Erythropoietin titers of plasma cannot be used to differentiate polycythemia vera from secondary polycythemia since the limit of sensitivity of our current bioassay technics is 50 mU, considerably higher than levels found in normal subjects and in patients with polycythemia. However, erythropoietin is relatively heat stable, and since abundant plasma is available from therapeutic phlebotomies it is possible to prepare and assay highly concentrated, erythropoietin-containing extracts. In 35 normal subjects, erythropoietin levels ranged from < 5 mU/ml (the limit of sensitivity) to 18 mU/ml with a mean of 7.8 mU/ml. In 21 patients with proved polycythemia vera, the levels were < 5 mU/ml in all. In 41 patients with suspected secondary polycythemia or polycythemia of unknown origin, the levels ranged from < 5 to 3,000 mU/ml. Three of the 11 patients with levels < 5 mU/ml were subsequently shown to have polycythemia vera. These results suggest that this refinement of the routine bioassay for erythropoietin may be of clinical importance in the differential diagnosis of polycythemia. © 1979.