Abstract
The use of insolubilized pure human intrinsic factor as binding protein in an isotope dilution assay for quantitation of serum cobalamins is described. The reference interval was 200—600 μmol/l. The coefficients of variation were 0.05 to 0.13 and the equilibrium constant for association to cyanocobalamin was 2 ± 1011 1/mol. The major advantage of the presented method is that intrinsic factor is kept saturated with cobalamin and is thereby stable until just prior to use.