Determination of Serum Immunoreactive Erythropoietin in the Investigation of Erythrocytosis

We assessed the diagnostic value of determinations of serum levels of immunoreactive erythropoietin in 90 patients referred for the investigation of a raised packed red-cell volume (hematocrit) and possible erythrocytosis (a red-cell volume greater than that predicted by weight, body-surface area, or both). The mean values for erythropoietin were 16 mlU per milliliter (range, 8 to 22) in patients with polycythemia rubra vera (n = 24),30-mlU per milliliter (range, 14 to 123) in patients with secondary erythrocytosis (n = 12), 27 mlU per milliliter (range, 13 to >400) in patients with erythrocytosis of unknown origin (n = 19), and 25 mlU per milliliter (range, 18 to 35) in normal controls (n = 25). The values in the patients with polycythemia rubra vera were lower than those in the other three groups (P