Human serum vitamin B12 assay methods--a review

The clinical importance of a reliable human serum vitamin B12 assay to aid the diagnosis of pernicious anemia (PA) cannot be overemphasized. Our review of the literature indicates that a reference method for the quantitation of serum vitamin B12 (serum B12) with the required accuracy, precision and rapidity has not been reported to-date. Controversies, debates and criticisms over human serum B12 assays (especially commercial kits) have been common-place. Various methods of quantitation of B12 reviewed in this communication include: microbiological, radioisotopic, high-performance liquid chromatography (HPLC) and the most recent radioimmunoassay (RIA) techniques. This review attempts to provide awareness of the limitations of these methods and establishes the base for eventual development of a B12 reference method in our laboratory.