Clinical Chemistry 56: 432-436, 2010. First published December 29, 2009; 10.1373/clinchem.2009.131524
This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
clinchem.2009.131524v1
56/3/432    most recent
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Google Scholar
Right arrow Articles by Hardlei, T. F.
Right arrow Articles by Nexo, E.
PubMed
Right arrow PubMed Citation
Right arrow Articles by Hardlei, T. F.
Right arrow Articles by Nexo, E.
Related Collections
Right arrow Endocrinology and Metabolism
(Clinical Chemistry. 2010;56:432-436.)
© 2010 American Association for Clinical Chemistry, Inc.

Endocrinology and Metabolism

Assessment of Vitamin B12 Absorption Based on the Accumulation of Orally Administered Cyanocobalamin on Transcobalamin

Tore Forsingdal Hardlei1,a, Anne Louise Mørkbak1, Mustafa Vakur Bor1, Lynn B. Bailey2, Anne-Mette Hvas3 and Ebba Nexo1

1 Department of Clinical Biochemistry, Aarhus University Hospital, Aarhus Hospital, Aarhus, Denmark; 2 Department of Clinical Biochemistry, Aarhus University Hospital, Skejby, Aarhus, Denmark; 3 Food Science and Human Nutrition Department, University of Florida, Gainesville, FL.

aAddress correspondence to this author at: Department of Clinical Biochemistry, Aarhus University Hospital, Skejby, Brendstrupgaardsvej 100, DK 8200 Aarhus N, Denmark. Fax 45-89-49-60-18; e-mail tore.forsingdal.hardlei{at}ki.au.dk.

Background: Vitamin B12, or cobalamin (Cbl), is absorbed in the intestine and transported to the cells bound to transcobalamin (TC). We hypothesize that cyanocobalamin (CNCbl) is absorbed unchanged, thereby allowing measurement of the complex of CNCbl bound to TC (TC–CNCbl) to be used for studying the absorption of the vitamin.

Methods: TC was immunoprecipitated from serum samples obtained from healthy donors at baseline and at 24 h after oral administration of three 9-µg CNCbl doses over 1 day. Cbl was released by treatment with subtilisin Carlsberg. The different forms of Cbl were isolated by HPLC and subsequently quantified with an ELISA-based Cbl assay.

Results: At baseline, the median TC–CNCbl concentration was 1 pmol/L (range, 0–10 pmol/L); the intraindividual variation (SD) was 1.6 pmol/L (n = 31). After CNCbl administration, the TC–CNCbl concentration increased significantly (P = 0.0003, paired t-test), whereas no major changes were observed in any of the other Cbl forms bound to TC (n = 10). Only a moderate additional increase in TC–CNCbl was observed with prolonged (5 days) CNCbl administration (n = 10). We designed an absorption test based on measuring TC–CNCbl at baseline and 24 h after CNCbl intake and established a reference interval for the increase in TC–CNCbl (n = 78). The median absolute increase was 23 pmol/L (range, 6–64 pmol/L), and the relative increase was >3-fold.

Conclusions: Our data demonstrate that CNCbl is absorbed unchanged and accumulates on circulating TC. We suggest that measuring TC–CNCbl will improve the assessment of vitamin B12 absorption.