Circulating Transferrin Receptor during Erythropoietin Medication of Anemic Patients with Rheumatoid Arthritis

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Abstract
Serum levels of the transferrin receptor (TfR) were monitored in 12 anemic patients with rheumatoid arthritis (RA) undergoing treatment with recombinant human erythropoietin (rHuEPO) for a 24-week period. Measurement of TfR was performed using an enzyme immunoassay. Compared to a mean pretreatment level of 4.2 mg/l (range 2.1-6.1 mg/l), there was an increase in the mean TfR concentrations from 2 weeks of treatment onwards to a maximum of 7.7 mg/l (range 2.1-12.3 mg/l) at 12 weeks (p < 0.01). Nine of the 12 patients responded to rHuEPO with an increase in blood hemoglobin concentration of 15 g/l or more. An increase in TfR levels was documented not only in the responders but also in the 3 nonresponders. We conclude that in anemic RA patients exogenous erythropoietin induces a swift and sustained increase in the serum concentration of TfR, which probably reflects increased expression of TfR on erythroblasts. This sustained elevation of TfR seems to occur even in patients who do not have an increase in their hemoglobin level.