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Licensed Unlicensed Requires Authentication Published by De Gruyter December 7, 2009

Determination of serum holotranscobalamin concentrations with the AxSYM active B12 assay: cut-off point evaluation in the clinical laboratory

  • Fabrizia Bamonti , Giovanna Antonella Moscato , Cristina Novembrino , Dario Gregori , Claudia Novi , Rachele De Giuseppe , Claudio Galli , Valentina Uva , Silvia Lonati and Rita Maiavacca

Abstract

Background: A reliable early marker is required for diagnosis of cobalamin deficiency. We calculated an appropriate holotranscobalamin (HoloTC) cut-off point for identifying cobalamin deficiency using an immunoenzymatic assay.

Methods: Determination of the cut-off threshold and correlation between HoloTC and the other diagnostic parameters routinely used for vitamin B12 deficiency [total vitamin B12 (tB12), folate, homocysteine] were measured in 250 routine blood specimens from 107 men (mean age 59.0±18.8 years) and 143 women (mean age 54.2±23.1 years). The inclusion criterion was serum tB12 concentration ≤221 pmol/L.

Results: Analytical performance results agreed with those reported by others. A weak correlation (R=0.42) was found between HoloTC and tB12. A 40 pmol/L cut-off threshold was chosen for HoloTC and the associated sensitivity and specificity was 0.86 and 0.66, respectively. Out of 250 tested samples, 126 showed tB12 concentrations 139–221 pmol/L (gray zone, GZ) and 124 had tB12 concentrations <139 pmol/L (low, L). Values less than the cut-off for HoloTC were present in 68.2% and 37.9% of cases in the GZ and L group, respectively (p<0.01), and in 53.2% of subjects.

Conclusions: Our results confirmed the analytical reliability of the AxSYM HoloTC assay. The method is adequate for routine use and a cut-off threshold of 40 pmol/L is appropriate for assessing cobalamin deficiency in populations with reduced tB12 values.

Clin Chem Lab Med 2010;48:249–53.


Corresponding author: Fabrizia Bamonti, Dipartimento Scienze Mediche, Università degli Studi di Milano, Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Fondazione IRCCS, Via F. Sforza, 35, 20122 Milan, Italy Phone: +390255033473, Fax: +390250320403,

Received: 2009-7-22
Accepted: 2009-9-24
Published Online: 2009-12-07
Published in Print: 2010-02-01

©2010 by Walter de Gruyter Berlin New York

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