DETERMINATION OF VITAMIN-B12 (COBALAMIN) IN SERUM AND ERYTHROCYTES BY RADIOASSAY, AND OF HOLO-TRANSCOBALAMIN-II (HOLO-TC-II) AND HOLO-HAPTOCORRIN (HOLO-TC-I AND III) IN SERUM BY ADSORBING HOLO-TC-II ON MICROFINE SILICA

We describe here a competitive inhibition radioassay of vitamin B12 in serum and erythrocytes, including differential radioassays to measure total corrinoids, "true" vitamin B12 (cobalamin), and vitamin B12 analogues in the assay of Lau et al.13 as modified by Kolhouse et al.15, in which the ligands are pure IF and R-binders. We also describe a method to determine holo-TC II (i.e., vitamin B12 on TC II) and holo-haptocorrin (i.e., vitamin B12 on TC I and TC III) by adsorbing TC II from haptocorrin (TC I and III) with microfine precipitate of silica (Quso). This procedure adds only one step to the vitamin B12 assay, and delineates negative vitamin B12 balance of patients at a very early stage of developing deficiency, well before the total serum vitamin B12 level falls below the laboratory range of normal. © 1991.