The use of Active-B12 (holotranscobalamin) as an accurate marker of vitamin B12 status was first proposed by Herzlich and Herbert  in 1988 (1) but subsequent early reports from other laboratories failed to establish the utility of Active-B12 (holoTC) (2). This can mostly be attributed to the unreliable nature of the early methods used. In most cases Active-B12 (holoTC) was estimated indirectly by the difference in total vitamin B12 levels before and after the adsorption of transcobalamin from the sample using various techniques, most of which were not totally selective. 

The cloning of the transcobalamin gene paved the way for new measurement methods based on specific transcobalamin antibodies (3) (4).  Very recently a novel monoclonal antibody was developed with 100-fold specificity for Active-B12 (holoTC) over the transcobalamin apo-protein (TC) which has allowed the development of simple, direct immunoassays for the quantitation of Active-B12 (holoTC) (5).  Such assays avoid the need for the various reduction/extraction/conversion steps employed by most vitamin B12 assays and so removing a possible cause of pre-analytical variability.

1. Herzlich B and Herbert V, Lab Invest., 1988; 58: 332-7.

2. Wickramasinghe SN and Ratnayaka ID, J Clin Pathol., 1996; 49: 755-8.

3. Ulleland M et al., Clin Chem., 2002; 48: 526-32.

4. Nexo E et al., Clin Chem., 2002 ; 48 : 561-2.

5. Orning L et al., Nutr Metab., 2006 ;3 ; 3.

News

Coming Soon !  The full video recording of the Euromedlab 2007 Active B12 workshop will be available in the next few weeks, register for your copy.

Live CME Web Conference on vitamin B12 deficiency, Prof. Ralph Green, Dec 13th 2007, register now.

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Meetings

8-11 December, 2007
American Society of Hematology, Atlanta, booth 544
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