Evaluation of intestinal iron absorption by indirect methods in patients on hemodialysis receiving oral iron and recombinant human erythropoietin.

Intestinal iron absorption was evaluated in 40 patients on hemodialysis therapy treated over 4 months with 105 mg/d of oral iron and recombinant human erythropoietin (rHuEPO). The effect of iron stores, erythropoietic activity (EA), and route of rHuEPO administration on absorption was evaluated. Iron was administered after basal determinations had been made and was stopped 15 days before obtaining the final determinations. Intestinal iron absorption was calculated by summing the increase in hemoglobin (Hb) iron (iron used for the synthesis of new Hb) and variations in estimated tissue iron reserves (reserves at the end of the study minus basal reserves). Markers of EA included soluble transferrin receptors (sTfRs) and erythron transferrin uptake (ETU). Iron losses caused by dialysis or normal obligatory iron losses were not measured. Hb levels increased from 8.38 +/- 1.4 to 10.75 +/- 1.5 g/dL (P < 0.05). sTfR levels reached their maximum value at 45 days (3.22 +/- 0.84 mg/mL; P < 0.05), and ETU increased from 40 +/- 26 to 61 +/- 39 micromol/L whole blood/d (P = 0.007). Intestinal iron absorption was 238 mg (interquartile range [Q75 to Q25], 255) at 2 months and 348 mg (Q75 to Q25, 475) at 4 months (P =0.02) and correlated positively with hematocrit at the end of the study (r = 0.826; P = 0.0001). No relationship between iron absorption and basal serum ferritin level or EA markers was observed. Intestinal iron absorption was similar regardless of the route of rHuEPO administration. In conclusion, intestinal iron absorption from medicinal iron covers erythropoietic requirements and allows Hb levels to increase significantly. It is proportional to the degree of efficient erythropoiesis reached and independent of tissue iron stores present before treatment, markers of EA, and rHuEPO administration route.