Holo-transcobalamin concentration and transcobalamin saturation reflect recent vitamin B12 absorption better than does serum vitamin B12.
Bor MV, Nexo E, Hvas AM.
Department of Clinical Biochemistry, AKH, Aarhus University Hospital, Norrebrogade 44, DK-8000 Aarhus C, Denmark. vakurbor@hotmail.com

BACKGROUND: We evaluated whether measurement of vitamin B(12)-saturated transcobalamin (holo-TC) concentrations or TC saturation (holo-TC:total TC) reflects active vitamin B(12) absorption in healthy individuals and patients after vitamin B(12) intake. METHODS: We obtained blood samples from 31 healthy individuals (age range, 25-57 years) before (days -1 and 0) and after (days 1, 2, and 6) oral administration of three 9-microg doses of vitamin B(12). The blood samples from seven patients (age range, 22-39 years) suspected to have decreased vitamin B(12) absorption were obtained before and 1 day after the vitamin B(12) intake. The blood samples were analyzed for vitamin B(12), total TC, and holo-TC. The TC saturation was calculated. RESULTS: Intraindividual variation was <13% for all measured values, as calculated from samples removed on day -1 and 0. In healthy individuals (n = 31) after intake of vitamin B(12), the maximum median (range) increase (as percentages and absolute values) was in TC saturation [52 (-2% to 128)% and 0.04 (0-0.23) as a fraction], closely followed by holo-TC concentrations [39 (0-108)% and 34 (0-149) pmol/L]. All but one healthy individual had an increase of >/=15% in these markers. Serum vitamin B(12) showed a smaller increase [14 (-8 to 51)% and 36 (-27 to 290) pmol/L]. After vitamin B(12) intake, three patients with Crohn disease had the lowest increases in holo-TC concentration (3, 7, and 14 pmol/L) and in TC saturation (0.004, 0.01, and 0.01) among patients and 30 healthy individuals. CONCLUSION: Holo-TC concentrations and TC saturation reflect normal vitamin B(12) absorption better than does serum vitamin B(12).

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