Articles: transcobalamins-metabolism.
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Eur. J. Clin. Invest. · May 2016
Association of a transcobalamin II genetic variant with falsely low results for the holotranscobalamin immunoassay.
The clinical use of holotranscobalamin (holoTC) testing to evaluate vitamin B12 status has increased in recent years. We present two patients (African Caribbean and Indian heritage), in which the holoTC assay indicated severe B12 deficiency (< 5 pmol/L). Additional clinical tests revealed that these patients had normal levels of total vitamin B12 in blood and unremarkable levels of two other markers of vitamin B12 status, homocysteine and methylmalonic acid. We hypothesized that these patients carry a variant in the transcobalamin gene (TCN2) that influences the most widely commercially available holoTC test - Active-B12 (Axis-Shield Diagnostics Ltd). ⋯ The impeded ability to detect normal levels of holoTC in these two patients may be due to this variant interfering with the detection of holoTC by one or both of the monoclonal antibodies currently employed in the Active-B12 test. Laboratories should be aware of this variant and use confirmatory tests when applicable.
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Annals of hematology · Apr 2014
Comparative StudyRole of serum holotranscobalamin (holoTC) in the diagnosis of patients with low serum cobalamin. Comparison with methylmalonic acid and homocysteine.
Plasma holotranscobalamin (holoTC) transports active cobalamin. Decreased levels of holoTC have been considered to be the earliest marker of cobalamin (Cbl) deficiency. In this work, holoTC was evaluated in low or borderline serum Cbl (LB12) and a concordance analysis was carried out with methylmalonic acid (MMA) and homocysteine (Hcy). ⋯ MMA/Hcy levels were not increased in a significant number of subjects with LB12 and low holoTC. This profile was found in iron deficiency. The significance of these changes remains to be clarified.
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Ann. Clin. Lab. Sci. · Jan 2013
Comparative StudySerum methylmalonic acid and holotranscobalamin-II as markers for vitamin B12 deficiency in end-stage renal disease patients.
Vitamin replacement, particularly B vitamins, remains an important concern in end-stage renal disease (ESRD) patients undergoing chronic hemodialysis. Serum markers such as methylmalonic acid (MMA) and holoTranscobalamin (holoTC) used to detect vitamin B12 deficiency are affected by impaired renal function which makes the interpretation of these biomarkers difficult in ESRD patients. We investigated the role renal failure has on MMA and holoTC concentrations and evaluated using MMA and/or holoTC to identify B12 deficient patients. ⋯ MMA is viable marker of B12 deficiency in ESRD patients. Holo TC has potential as a supplementary marker with MMA to predict the response of vitamin B12 supplementation. Future studies on MMA and B12 should be done to confirm these findings in larger cohorts and to identify individuals who may benefit from vitamin B12 supplementation.
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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. ⋯ 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 tB(12) values.
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Ann. Clin. Lab. Sci. · Jan 2009
Holotranscobalamin as an indicator of vitamin B12 deficiency in gastrectomized patients.
Transcobalamin-bound vitamin B(12), or holotranscobalamin (HoloTC), a biologically active form, is believed to be a sensitive marker of vitamin B(12) deficiency. We investigated the prevalence of vitamin B(12) deficiency in gastrectomized patients using HoloTC and total vitamin B(12) to determine the diagnostic utility of HoloTC. We enrolled 128 gastrectomized patients and measured serum HoloTC, total vitamin B(12), homocysteine (Hcy), and complete blood count (CBC). ⋯ The patients with both low total vitamin B(12) and low HoloTC had significantly higher Hcy concentrations than those with either normal total vitamin B(12) or normal HoloTC. Although a quarter of gastrectomized patients had low HoloTC, some of these had normal total vitamin B(12) concentrations. Our study suggests that serum HoloTC is a more sensitive marker than total vitamin B(12) in diagnosing vitamin B(12) deficiency.