Holotranscobalamin as an Indicator of Dietary Vitamin B12 Deficiency
Zouë Lloyd-Wright1, Anne-Mette Hvas2, Jan Møller3, Tom A.B. Sanders1,a and Ebba Nexø2
1 Nutrition Food & Health Research Centre, King’s College London, Franklin-Wilkins Bldg., 150 Stamford St., Waterloo, London SE1 9NN, United Kingdom;2 Department of Clinical Biochemistry, AKH, Aarhus University Hospital, DK-8000 Aarhus C, Denmark;3 Depa

We report that serum holotranscobalamin (holoTC) compares favorably with serum vitamin B12 for identifying vegans likely to have vitamin B12 deficiency as judged by measurements of the metabolites methylmalonic acid (MMA) and homocysteine (tHcy). We also report that measurement of holoTC may possibly replace combined testing with serum vitamin B12 (B12), MMA, and tHcy in this population.

Recently, two new markers for vitamin B12 deficiency, holoTC (TC saturated with vitamin B12) and the related TC saturation (the fraction of total TC present as holoTC), have been introduced (1)(2)(3). Approximately 30% of circulating B12 is attached to TC, whereas the major part of B12 is attached to another protein, haptocorrin. Because only B12 attached to TC (holoTC) is able to enter all the cells of the body, holoTC may be a more useful marker than total B12 in serum.

We compared holoTC with the tests currently used for diagnosis of vitamin B12 deficiency, i.e., B12, MMA, and tHcy, in vegan men, whose diets are devoid of food of animal origin (and thus low in vitamin B12) and who thus are susceptible to developing B12 deficiency.

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