Single value of serum transferrin receptor is not diagnostic for the absence of iron stores in anaemic patients with rheumatoid arthritis.

Serum transferrin receptor (sTfR) concentrations were measured in anaemic patients with rheumatoid arthritis (RA). Serum transferrin receptor concentrations were positively correlated with the percentage of hypochromic cells and negatively correlated with MCH. There was a weak correlation with serum ferritin (sFn) concentration but not with reticulocyte count. Thus, high concentrations of sTfR indicate iron-deficient erythropoiesis rather than levels of storage iron in the tissues. Patients were divided into three groups on the basis of sFn concentration: those with probable tissue iron deficiency, those with adequate iron stores and those with intermediate values of sFn which did not allow classification. The median sTfR concentration was significantly higher in the iron-deficient group than in the other two groups but because of overlap between the three groups, a single sTfR value was of limited value in determining the level of storage iron in an individual with RA.