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This Article Full Text (PDF) All Versions of this Article: clinchem.2005.055509v1 51/11/2151    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bor, M. V. Articles by Nexo, E. Search for Related Content PubMed PubMed Citation Articles by Bor, M. V. Articles by Nexo, E.

Received on June 5, 2005
Accepted on August 23, 2005

Nutrition

Nonradioactive Vitamin B₁₂ Absorption Test Evaluated in Controls and in Patients with Inherited Malabsorption of Vitamin B₁₂

Mustafa Vakur Bor ^1*, Mualla Çetin ², Selin Aytaç ², Çidem Altay ², Ebba Nexo ³

¹ Department of Clinical Biochemistry, NBG, AS, and Department of Clinical Biochemistry, Aalborg Hospital, Aarhus University Hospital, Aarhus, Denmark
² Department of Pediatrics, Faculty of Medicine, Hacettepe University, Ankara, Turkey
³ Department of Clinical Biochemistry, NBG, AS

^* To whom correspondence should be addressed. E-mail: vakurbor{at}hotmail.com.

Background: Current tests for evaluation of vitamin B₁₂ absorption are problematic because they involve the use of radioactively labeled vitamin B₁₂. We describe a vitamin B₁₂ absorption test that circumvents this problem.

Methods: We measured cobalamin or transcobalamin saturated with cobalamin (holo-TC) 24 h after three 9-µg doses of vitamin B₁₂ given orally at 6-h intervals. We studied 17 patients with inherited malabsorption of vitamin B₁₂ attributable to Imerslund-Grasbeck syndrome (n = 13) or intrinsic factor deficiency (n = 4), their obligate heterozygous biological parents (n = 19), and healthy controls (n = 44).

Results: In the patients, the median (range) change of holo-TC after the B₁₂ load was not significant [1 (-42 to 5) pmol/L], nor was the change of cobalamin [-3 (-32 to 22) pmol/L], consistent with a lack of measurable active or passive absorption. In controls, however, the median (range) increases of holo-TC and cobalamin were 26 (-6 to 63) pmol/L and 41 (-37 to 109) pmol/L, respectively. Similarly, the parents showed increases of 23 (-2 to 47) pmol/L and 27 (-15 to 94) pmol/L. The mean areas under the ROC curves (95% confidence intervals) were 0.97 (0.93-1.0) for holo-TC and 0.87 (0.79-0.94) for cobalamin, distinguishing patients from controls. At a cutoff of 6 pmol/L for holo-TC, the diagnostic sensitivity (95% confidence interval) was 100 (81-100)%, and the diagnostic specificity was 92 (82-97)%.

Conclusion: Measurement of holo-TC after administration of vitamin B₁₂ is a promising approach for evaluating vitamin B₁₂ absorption.

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