CLINICAL UTILITY OF THE SOLUBLE TRANSFERRIN RECEPTOR AND COMPARISON WITH SERUM FERRITIN IN SEVERAL POPULATIONS

Soluble transferrin receptor (sTfR) and ferritin concentrations were m easured in a variety of clinical settings to compare the ability of th ese two tests to identify iron deficiency. Among 62 anemic patients wh o either had a bone marrow aspirate performed or had a documented resp onse to iron therapy, the diagnostic sensitivity and specificity of sT fR (at a diagnostic cutoff of >2.8 mg/L) were 92% and 84%, respectivel y, with a positive predictive value of 42% in this population. Ferriti n (less than or equal to 12 mu g/L) had a sensitivity of 25% and a spe cificity of 98%. However, the sensitivity and specificity of ferritin could be improved to 92% and 98%, respectively, by using a diagnostic cutoff value of less than or equal to 30 mu g/L, resulting in a positi ve predictive value of 92%. Ferritin and sTfR were also measured in 26 7 outpatient samples and 112 medical students. In the outpatient group , the two tests agreed in 73% of the samples; however, 25% of the samp les had ferritin values >12 mu g/L and increased sTfR. Among the medic al students, there was 91% agreement between the two tests, but 7% of the samples had ferritin less than or equal to 12 mu g/L and normal sT fR. Together, these data suggest that measurement of sTfR does not pro vide sufficient additional information to ferritin to warrant routine use. However, sTfR may be useful as an adjunct in the evaluation of an emic patients, whose ferritin values may be increased as the result of an acute-phase reaction.