Holo-Transcobalamin Concentration and Transcobalamin Saturation Reflect Recent Vitamin B12 Absorption Better than Does Serum Vitamin B12

Abstract

Abstract Background: We evaluated whether measurement of vitamin B12-saturated transcobalamin (holo-TC) concentrations or TC saturation (holo-TC:total TC) reflects active vitamin B12 absorption in healthy individuals and patients after vitamin B12 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-μg doses of vitamin B12. The blood samples from seven patients (age range, 22–39 years) suspected to have decreased vitamin B12 absorption were obtained before and 1 day after the vitamin B12 intake. The blood samples were analyzed for vitamin B12, 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 B12, 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 B12 showed a smaller increase [14 (−8 to 51)% and 36 (−27 to 290) pmol/L]. After vitamin B12 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 B12 absorption better than does serum vitamin B12.