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

¹ Department of Clinical Biochemistry, AKH, Aarhus University Hospital, Norrebrogade 44, DK-8000 Aarhus C, Denmark.

^aAuthor for correspondence. Fax 45-89493060; e-mail vakurbor{at}hotmail.com.

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.

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