Erythropoietin deficiency causes anemia in nephrotic children with normal kidney function

Anemia in persistent nephrotic syndrome (NS) has been described in a few case reports but has not been studied systematically. We present a group of 19 children with NS who developed anemia before the deterioration of kidney function. The aim of our study is to determine whether erythropoietin (EPO) and/or iron deficiency are causative factors and to evaluate the effect of EPO replacement therapy. Serum EPO levels, iron status, and vitamin B(12) concentrations were measured in nephrotic patients with anemia (NS-A) and compared with those of nephrotic children with normal hemoglobin (Hb) levels (NS-NHb; n = 13). Two control groups consisted of age-matched patients without kidney disease or hypoxemia with either iron deficiency anemia (IDA; n = 19) or normal Hb concentrations (NHb; n = 16). Most NS-A patients experienced persistent steroid-resistant NS, whereas most NS-NHb children had steroid-responsive NS. Although serum iron, ferritin, and B(12) levels were significantly lower in NS-A children, appropriate replacement therapy that resulted in normalization of ferritin and/or cobalamin levels did not lead to correction of the anemia. NS-A patients had greater EPO levels than those without anemia (21.6 +/- 3.3 versus 5.5 +/- 0.8 IU/L; P: < 0.001), but their response to anemia was inappropriately low compared with IDA children (EPO, 94.6 +/- 15.1 IU/L) despite similar Hb concentrations. EPO therapy for 4 to 9 months in 6 NS-A children with Hb levels less than 9 g/dL led to resolution of the anemia. In conclusion, anemia is a common feature of persistent NS that develops before the deterioration of kidney function. Depletion of iron stores may contribute to the development of anemia, but iron replacement therapy is ineffective. Nephrotic patients have EPO deficiency with a blunted response to anemia. The EPO deficiency is amenable to EPO therapy, which is recommended for this group of patients.