Serum Transferrin Receptor Value as a Universal Indicator of Erythropoietic Activity.

The serum transferrin receptor (sTfR) is thought a sensitive and quantitative parameter of tissue iron deficiency as well as an indicator of erythropoietic activity. This study was aimed at the verification of a hypothesis that sTfR is a general indicator of erythropoiesis regardless whatever the cause is. A total of 173 patients in heterogeneous diseases who underwent bone marrow study as a workup for anemia were measured for sTfR, reticulocyte maturity index (RMI), erythroid element proportion of bone marrow cells, and other hematologic parameters (hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin concentration, red cell distribution width, absolute reticulocyte count). By immunoenzymometric method sTfR was measured using IDeATMcTfR kids (Orion Diagnostica, Orion, Finland). Reticulocyte count and proportion was measured manually by one expert examiner after standard blood smear and stain. Reticulocyte subpopulation was automatically analyzed by flow cytometry using R-3000 TM (Sysmex, TOA, Japan). RMI was calculated from the equation of (medium fluorescent reticulocyte fraction + high fluorescent reticulocyte fraction) X 100 / low fluorescent reticulocyte fraction. Correlation analysis was done among the variables including sTfR, RMI, erythroid element proportion of bone marrow cells, and other hematologic parameters using SAS 6.12 soft ware. The analysis was carried out for the whole 173 patients to see the general trends and repeated for 4 groups of disease category, arbitrarily divided to group 1 (n=33, iron deficiency or or disease with no predisposition to anemia of chronic disease), group 2 (n=53, hematologic malignancies), group 3 (n=44, solid tumors), and group 4 (n=43, chronic or infectious disease) to see if the trends may be affected by specific diseases. The results showed a solid correlation of sTfR with RMI as well as erythroid precursors in bone marrow, not only in the whole patient population (e.g. sTfR vs RMI, R=0.587, p=0.0001) but also in individual groups (e.g. sTfR vs RMI, R=0.48, p=0.005 in group 1, R=0.69, p=0.0001 in group 2, R=0.58, p=0.0001 in group 3, R=0.81, p=0.0001 in group 4). These findings indicated the significance of sTfR is valid under any clinical setting as a universal indicator of hematopoietic activity. The sTfR can be used as a useful parameter for monitoring of erythropoiesis in a variety disease.