New Enzymatic Assay of Iron in Serum

A new enzymatic method for assaying iron in serum sam-ples, suitable for automated analyzers, is reported. Three reagent mixtures are used: dilution buffer (pH 3.0; ascor-bate), reagent 1 (pH 6.7; apoaconitase), and reagent 2 (pH 7.7; citrate, magnesium, and isocitrate dehydrogenase). Sera are diluted with dilution buffer. Fe3 is liberated from transferrin in sera under acidic conditions, and then re-duced by ascorbate. Reagent 1 is added to diluted speci-mens, and apoaconitase is reactivated by Fe2 at neutral pH. The resulting solutionsare mixed with reagent 2, so that holoaconitase hydrolyzes citrate to isocitrateand the isocitrate and NADP are converted to 2-oxoglutarate, NADPH, and CO2. Serum iron is determined linearlyup to 70 p.mol/L, with within-run CVs 2.4 % and day-to-day CVs 2.9%. This method (y) givesresultscorrelatingwith thos