Development of a specific radioimmunoassay for vitamin B12 and its application in the diagnosis of cobalt deficiency in sheep.

A radioimmunoassay (RIA) for vitamin B12 is described. Antisera were raised in rabbits using a conjugate between 5'-O-succinyl cyanocobalamin and chicken serum albumin. The antibody is largely specific for the beta (upper) face of the vitamin B12 molecule. The RIA can detect vitamin B12 down to concentrations of 37 pmol/L and correlated well (r = 0.980, p less than 0.001) with a commercial radioassay. The use of this RIA, together with an assay for plasma methylmalonic acid, in the diagnosis of cobalt/vitamin B12 deficiency in sheep is described.