Red blood cell precursor mass as an independent determinant of serum erythropoietin level

Serum erythropoietin (sEpo) concentration is primarily related to the rate of renal production and, under the stimulus of hypoxia, increases exponentially as hemoglobin (Hb) decreases. Additional factors, however, appear to influence sEpo, and in this work, we performed studies to evaluate the role of the red blood cell precursor mass. We first compared the relationship of sEpo with Hb in patients with low versus high erythroid activity. The first group included 27 patients with erythroid aplasia or hypoplasia having serum transferrin receptor (sTfR) levels <3 mg/L (erythroid activity <0.6 times normal), while the second one included 28 patients with β-thalassemia intermedia having sTfR levels > 10 mg/L (erythroid activity > 2 times normal). There was no difference between the two groups with respect to Hb (8.3 ± 1.6 v 8.0 ± 1.3 g/dL, P > .05), but sEpo levels were notably higher in patients with low erythroid activity (1,601 ± 1,542 v 235 ± 143 mU/mL, P <.001). In fact, multivariate analysis of variance (ANOVA) showed that, at any given Hb level, sEpo was higher in patients with low erythroid activity (P