Soluble transferrin receptor (sTfR) concentration quantified using two sTfR kits: analytical and clinical performance characteristics

We compared the analytical and clinical performance characteristics of the Rameo and R&D Systems enzyme-linked immunosorbent assays (ELISAs) for quant ifying serum levels of soluble transferrin receptor (sTfR). In addition, we determined both the number of samples required to determine the true indiv idual mean sTfR concentration for a single individual and the critical diff erence (CD) between serial measurements that indicates a statistically sign ificant change in sTfR concentration, sTfR concentration was determined in 127 serum samples selected retrospectively from males (n=32) and non-pregna nt (n=40) and pregnant women (n=55). Intra- and inter-assay precision for b oth methods was good (CV values 5-10%) to excellent (CV values <5%) over a wide range of sTfR concentrations. Correlation between these methods was go od (r=0.93); however, sTfR values by the R&D hit were <similar to>2.9 times higher than values obtained using the Rameo hit on the same serum samples. Nevertheless, receiver-operator characteristic (ROC) curve analysis demons trated that the diagnostic accuracy of both assays in discriminating betwee n patients with iron-deficiency anemia (IDA) or anemia of chronic disease ( ACD) was high (area-under-the-curve (AUC) values >0.95) and not significant ly different (P=0.480). We determined that a minimum of 8 samples are requi red to determine an individual's true sTfR concentration, while a >40% diff erence between serial sTfR measurements would he required to indicate a sta tistically significant change in sTfR concentration. We concluded that both the Rameo and R&D Systems sTfR methods have similar analytical and clinica l performance characteristics and were likely to be equally useful in discr iminating between patients with biochemically defined IDA ol ACD. (C) 2001 Elsevier Science B.V. All rights reserved.