Holotranscobalamin as an indicator of dietary vitamin B12 deficiency.

Abstract

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. The vegan men were recruited from two sources: 100 (of a subset of 233) vegan men enrolled in the Oxford cohort of the EPIC study (European Prospective Investigation into Cancer and Nutrition) between 1993 and 1997 for whom measurements of B12 had been performed at enrollment [mean (range) B12 at enrollment, 170 (67–397) ng/L; mean (range) age at recruitment, 49 (27–78) years]; and 72 men (of a total of 96 respondents) who were members of the London Vegan Society between 2001 and 2002 [mean (range) age, 38 (18–70) years]. The vegan men had consumed no food of animal origin for a mean (range) of 24 …