Performance characteristics of the Dimension RxL iron and total iron-binding capacity methods

Background: Measurements of serum iron and total iron-binding capacity (TIBC) can be used to aid the diagnosis of iron deficiency and iron overload states. A variety of different methods for these measurements are commercially available. Methods: Linearity, imprecision and hemoglobin interference of homogeneous iron and TIBC methods on a Dimension® RxL analyzer were assessed. Method comparison studies were performed with a Vitros® 950 analyzer. Results: The Dimension RxL iron method was linear from 40 to 1000 μg/dl. The coefficient of variation of the iron and TIBC methods were <4% and <2%, respectively, at iron concentrations of 68 and 228 μg/dl and TIBC concentrations of 206 and 384 μg/dl. Comparison of the Vitros 950 and Dimension RxL iron methods gave a slope of 0.97, an intercept of 6.0 and r=0.99. Corresponding results for the TIBC methods were 1.02, -6.6 and r=0.97, respectively. Simulation of acute iron overload in vitro did not produce the same effect on TIBC measurements as in vivo overload. Iron recovery by the Dimension RxL method was reduced 40-60% by the addition of deferoxamine at a concentration of 200 μmol/l. Conclusions: The Dimension RxL assay provides acceptable measurements of iron and TIBC in routine patient samples. Iron measurements are unreliable in the presence of deferoxamine.