Radioisotopic assay of serum vitamin B₁₂ with the use of DEAE cellulose

A radioisotopic assay of vitamin B₁₂ in serum is described. The assay is specifically designed to achieve maximum accuracy in the low serum B₁₂ range in order to better delineate B₁₂-deficient sera from sera with low, but normal, values of B₁₂. The technique, utilizing the principle of saturation analysis, employs Cobalt-57 B₁₂ added to the unknown sera as a tracer for the subsequent determination of per cent recovery of endogenous B₁₂. Endogenous protein-bound B₁₂ is liberated from the test sera, and a suitable quantity of B₁₂-binding protein from pooled sera is added. The bound B₁₂ is quickly separated from the free B₁₂ by batchwise DEAE cellulose adsorption, and the per cent of protein-bound B₁₂ concentration is determined. The procedure is reasonably rapid, is replicable, and is especially suitable for the clarification of borderline B₁₂-deficient states.