Rapid Charcoal Assay for Intrinsic Factor (IF), Gastric Juice Unsaturated B12 Binding Capacity, Antibody to IF, and Serum Unsaturated B12 Binding Capacity

Abstract The principle of the dialysis assays for intrinsic factor (IF) and antibody to IF was integrated with the demonstration that protein-coated charcoal adsorbs only free and not bound B12, in a single rapid method for 4 separate assays: (1) assay of IF, (2) assay of gastric juice unsaturated B12 binding capacity, (3) assay of serum antibodies to IF and (4) assay of serum unsaturated B12 binding capacity. The method is sensitive, accurate, reproducible, and can easily be completed within an hour. The simplicity and ready availability of reagents and equipment lends itself to ready adoption in any clinical laboratory using radioisotopes. The charcoal particle is considered as a solid microsponge, and its coat of albumin, other protein, carbohydrate, or other large molecule as a molecular sieve surrounding the sponge. The whole constitutes a system of "instant dialysis," with a wide range of applications in the separation of large from small molecules.