Transferrin receptor expression on reticulocytes as a marker of iron status in dialyzed patients

Erythropoietin therapy should be accompanied by an adequate iron supply in order to avoid functional iron deficiency (FID) related to enhanced erythropoiesis. Therefore, accurate monitoring of the body's iron homeostasis is needed. This study was conducted to investigate whether transferrin receptor (TfR) expression on reticulocytes can reflect iron status in patients with chronic renal failure (CRF).

TfR expression [antibody binding capacity (ABC)] and the proportion of TfR positive reticulocytes (%TfR+ Ret) relative to all reticulocytes were measured by a quantitative flow cytometric method at baseline and at 3 weeks in 34 dialysis patients. Iron status (plasma ferritin and soluble TfR) and hemoglobin (Hb) with advanced cellular indices, such as the percentage of hypochromic reticulocytes (%HYPOr) and cellular Hb in reticulocytes (CHr), were also analyzed.

Patients with FID had significantly higher TfR ABC and %TfR+ Ret compared with patients with replete iron status (p=0.034 and p=0.006, respectively). In patients whose Hb concentrations showed a reduction, the mean increase (3 weeks- baseline) in TfR ABC was four-fold higher and %TfR(+)Ret was three-fold higher when compared with patients whose Hb was stable or had increased. The changes in TfR expression correlated significantly with the changes in reticulocyte indices [CHr (negatively), %HYPOr (positively)] and plasma ferritin (negatively).

Reticulocyte TfR expression reflected the changes in the Hb level and the iron availability at the cellular level, and therefore it might be useful in the assessment of iron status in patients with CRF.