• Fabrizia Bamonti, Giovanna Antonella Moscato, Cristina Novembrino, Dario Gregori, Claudia Novi, Rachele De Giuseppe, Claudio Galli, Valentina Uva, Silvia Lonati, and Rita Maiavacca.
• Dipartimento Scienze Mediche, Università degli Studi di Milano, Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Fondazione IRCCS, Milan, Italy. fabrizia.bamonti@unimi.it
• Clin Chem Lab Med. 2010 Feb 1; 48 (2): 249-53.

BackgroundA 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.MethodsDetermination of the cut-off threshold and correlation between HoloTC and the other diagnostic parameters routinely used for vitamin B(12) deficiency [total vitamin B(12) (tB(12)), 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 tB(12) concentration ResultsAnalytical performance results agreed with those reported by others. A weak correlation (R=0.42) was found between HoloTC and tB(12). 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 tB(12) concentrations 139-221 pmol/L (gray zone, GZ) and 124 had tB(12) 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.ConclusionsOur 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 tB(12) values.

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