THE RELATION BETWEEN CHEMICALLY MEASURED TOTAL IRON-BINDING-CAPACITY CONCENTRATIONS AND IMMUNOLOGICALLY MEASURED TRANSFERRIN CONCENTRATIONSIN HUMAN SERUM

We sought to determine if serum total iron-binding capacity (TIBC) is equivalent to serum transferrin (TRF) so that a low-cost colorimetric chemical assay for unsaturated iron-binding capacity (UIBC) could be s ubstituted for a high-cost immunologic assay for TRF. Our study design included independent and blinded measurements of UIBC, serum iron, an d TRF concentrations in human serum samples. Data from five independen t correlation studies carried out at three different Quest Diagnostics laboratories were combined into one data set containing 570 paired re sults for TIBC and TRF. r(2) was 0.941 when three outliers were elimin ated from the 570-sample data set. Scatter about the regression line w as fully accounted for by the CVs for the TIBC and TRF assays. When ea ch test is measured precisely and without bias, the ratio of TIBC (mu mol/L) to TRF (g/L) in SI units is close to the theoretically expected value of 25.0.