Modification of Fully Automated Total Iron-binding Capacity (TIBC) Assay in Serum and Comparison with Dimension TIBC Method

Abstract

We previously reported the development of a fully automated assay for total iron-binding capacity (TIBC) in serum, using a multipurpose automated analyzer. However, this method requires four different reagents and is thus useful only with a limited number of available analyzers. We simplified our original assay and compared the analytical performance of the modified method with that of a commercial, fully automated TIBC assay (Dimension TIBC assay). We simplified our original method to require only three reagents. Calibration was also altered and was performed with human transferrin standard solutions. An advantage of this method is that it does not require separation of excess unbound iron after the first step of transferrin saturation. Unbound iron is eliminated by formation of a complex with the chromogenic reagent ferrozine in the second step. Iron dissociated from transferrin by acidic pH reacts with ferrozine to form a colored complex in the final step, and the increase in absorbance at 570/660 nm is directly proportional to the TIBC measured. TIBC values were determined for 49 healthy individuals and 148 patients with this modified TIBC assay and with a commercial, fully automated TIBC method (Dimension clinical chemistry system), and calculation of TIBC based on the sum of the serum iron and unsaturated iron-binding capacity was performed for 97 patients. The within-run CVs for the modified TIBC assay and the Dimension TIBC assay were <4.8% and <2.4%, and the between-run CVs were 1.2% and 1.7%, respectively. The dilution curves were linear for TIBC values up to at least 180 micromol/L with both methods. TIBC values obtained by our method were linearly correlated with serum transferrin concentrations (r = 0.984; S(y/x) = 3.18 micromol/L; P <0.001). The correlation between the values obtained with the present method (y) and those obtained with the Dimension TIBC method (x) was y = 1.04x + 1.19 micromol/L (r = 0.985; S(y/x) = 2.47 micromol/L), and with the calculation method (x) was y = 1.18x + 2.62 micromol/L (r = 0.976; S(y/x) = 3.27 micromol/L). Our modified, fully automated TIBC assay performed similarly to the Dimension TIBC assay and is adaptable for use with many multipurpose automated analyzers.