Kinetics of reticulocyte maturity fractions and indices and iron status during therapy with epoetin beta (recombinant human erythropoietin) in cardiac surgery patients.

We evaluated the changes in reticulocyte maturity fractions and indices, as measured by flow cytometry, during preoperative treatment with recombinant human erythropoietin (epoetin beta) in cardiac surgery patients. A total of 72 patients was enrolled in this double-blind, randomized, placebo-controlled clinical trial and assigned to the two treatment groups (5 x 500 U/kg bodyweight epoetin beta or placebo intravenously over 14 days preoperatively). Therapy with epoetin beta produced continuous increases in hematocrit/hemoglobin, in the most mature fraction of reticulocytes (LR), and in reticulocyte count. In the first treatment week there were parallel increases in the fraction of most immature reticulocytes (HR) and in the reticulocyte mean cell volume. During the second week of treatment the reticulocyte mean cell hemoglobin content (CHr) decreased, but CHr was independent of all iron parameters, affecting neither the reticulocyte fractions nor the hematocrit/hemoglobin increase. The total preoperative rise in hematocrit correlated with the rises in LR fraction (P = 0.0270) and reticulocyte count (P = 0.0486) during the first week of treatment. Whereas in the epoetin beta patients the preoperative change in HR fraction showed negative correlations with transferrin saturation at baseline (P = 0.0058) and with the preoperative change in iron (P = 0.0113), the preoperative change in the LR fraction correlated positively with transferrin at baseline (P = 0.0115). Postoperatively, the reticulocyte parameters revealed that the onset of increased stimulation of erythropoiesis did not occur in the placebo patients until the second postoperative day, whereas erythropoietic activity in the epoetin beta patients was much higher during the postoperative period as well, as a result of the preoperative stimulation of erythropoiesis. The reticulocyte parameters measured by flow cytometry permitted an objective analysis of erythropoietic activity during treatment with epoetin beta and in all patients postoperatively. Further studies in various types of epoetin beta therapy are needed in order to clarify the value of these reticulocyte parameters for identification of iron deficiency and optimization of epoetin beta treatment regimen.