A METHOD FOR DETERMINATION OF VITAMIN B12 IN SERUM BY RADIOASSAY

A radioisotopic method for determining the vitamin B12 concentration in serum was studied. The method is based on the principle of saturation analysis. After extraction of the vitamin B12 from the unknown sample a test serum is added, providing the B12-binding proteins. The bound fraction is then measured after adsorption of the binding proteins to DEAE-cellulose. The B12-binding proteins of the sample were completely removed by boiling in acetate buffer pH 4.6. A technique for evaluating the optimal amount of the test serum added per analysis is described. Optimal conditions for the adsorption of the binding proteins of test serum on DEAE cellulose was obtained by using a Tris buffer. The method requires only 0.2 ml of serum per analysis. With normal serum vitamin B12 concentrations the error for a single determination was about 3%. The serum concentrations determined by the method were in close agreement with the microbiological assays. The method achieves maximum accuracy within the concentration range of interest for the diagnosis of vitamin B12 deficiency. © 1969.