CHAPTER 26: Analysis of Cobalamins (Vitamin B₁₂) in Human Samples: An Overview of Methodology

Valid cobalamin analysis in human serum is important to clarify nutritional status and to diagnose cobalamin deficiency. Refined methods suitable for both routine and research purposes have been established, but in order to benefit from these assays, it is important to realise their strengths and limitations and to be aware of new developments. Serum cobalamin includes liberation of cobalamin from binding proteins, conversion of the various forms of cobalamin into a single form, and finally quantification often employing microbiological or protein binding assays. Standardized microbiological and protein binding assays have been developed for measurement of total cobalamin in serum, but several aspects should be considered when using these assays. For example, although different protein binding assays use comparable principles and reagents, they respond differently to samples containing a high concentration of cobalamin binding proteins such as human milk. A number of other methods are available for measuring total cobalamin and the individual forms of both cobalamin and other cobalamin analogues. These are used for cobalamin analysis in food samples and for research purposes. A recent development is to measure serum cobalamin bound to the protein transcobalamin. This parameter may be a better marker than total serum cobalamin to identify cobalamin deficiency.