Markers of masked iron deficiency and effectiveness of EPO therapy in chronic renal failure.

Recombinant erythropoietin (rHuEPO) is well established in the management of anemia of chronic renal disease. However, a number of clinical issues, including the best laboratory indicators of an imminent marrow response to rHuEPO replacement, the ideal measurements to detect masked iron deficiency, and optimal methods of iron replacement, remain unanswered. To investigate these issues, studies were performed in anemic chronic hemodialysis patients. A number of standard hematologic measurements in addition to automated reticulocyte counts (Sysmex R-1000) and serum transferrin receptors (TfR) were obtained in these patients. A response to initiation of rHuEPO administration could be predicted if the serum TfR concentration was less than 6 mg/L (normal, 3.8 to 8.5 mg/L). In patients on rHuEPO, an imminent hemoglobin response to an increased rHuEPO dose could be predicted after 1 week based on a greater than 20% increase from baseline in the serum TfR or absolute reticulocyte count, with a sensitivity of 92%. In patients on rHuEPO replacement with serum ferritin levels greater than 30 microg/L, none of the panel of tests, including serum TfR, reliably detected masked iron deficiency. In a long-term study over 5 months in patients on a stable maintenance dose of EPO, a gradual decline in total body iron occurred, even in subjects with initial adequate iron stores, and despite taking 50 mg elemental iron daily as oral ferrous sulphate. The serum TfR is useful for predicting a hemoglobin response when initiating rHuEPO therapy, and combined with automated reticulocyte counting it is valuable for predicting a hemoglobin response when increasing the dose of rHuEPO. The serum TfR loses its specificity for detecting tissue iron deficiency in patients on maintenance rHuEPO therapy because of increased erythropoiesis, which itself raises serum TfR levels.