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General Clinical Chemistry |
1 Department of Pharmacology, University of Oxford, Oxford, United Kingdom.
2 Institute of Medicine, Section of Pharmacology, University of Bergen, Institute of Basic Medical Sciences, Department of Nutrition, University of Oslo, Oslo, Norway.
3 Department of Anaesthesia and Intensive Care, Haukeland University Hospital, Bergen, Norway.
4 Department of Clinical Biochemistry, Norrebrogade, Aarhus Sygehus, Aarhus University Hospital, Aarhus C, Denmark.
aAddress correspondence to this author at: Oxford Centre for Gene Function, University Laboratory of Physiology, University of Oxford, Parks Rd, Oxford OX1 3P, United Kingdom. E-mail helga.refsum{at}physiol.ox.ac.uk.
Background: We developed microbiological assays (MBAs) to identify determinants and to establish reference values for cobalamin bound to transcobalamin [holotranscobalamin (holoTC)] and total TC in plasma.
Methods: We captured holoTC with magnetic beads with TC antibodies and used a conventional MBA for cobalamin measurements. Total TC was determined as holoTC after TC was saturated with cyanocobalamin. The new assays were compared with published methods. Determinants and reference values were determined in 500 blood donors, ages 18–69 years.
Results: Determination of cobalamin, holoTC, and TC by MBA required <150 µL. HoloTC and TC by MBA correlated with holoTC by RIA (r = 0.95) and TC by ELISA (r = 0.79), respectively. Between-day CVs for holoTC and total TC were 4%–9%. Women had lower holoTC than men, but only at age 
45 years. In multivariate regression analyses, holoTC was positively associated with age (in women only), creatinine (in men only), and plasma concentrations of total TC, folate, and cysteine, but inversely correlated with homocysteine and methylmalonic acid. For all study participants, total TC was associated with holoTC and number of TCN2 766C alleles; in female participants only, total TC was also associated with age, homocysteine, and cysteine. Reference values were 670–1270 pmol/L for TC and 42–157 pmol/L for holoTC, but they differed according to age and sex.
Conclusions: Our MBAs for TC and holoTC required low plasma volume and performed acceptably compared with other methods. Determinants of holoTC and TC differed between men and women and according to age. Separate reference intervals for holoTC should be considered in younger women.
The following articles in journals at HighWire Press have cited this article:
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  G. Moroni, C. Novembrino, S. Quaglini, R. De Giuseppe, B. Gallelli, V. Uva, V. Montanari, P. Messa, and F. Bamonti Oxidative stress and homocysteine metabolism in patients with lupus nephritis Lupus, January 1, 2010; 19(1): 65 - 72. [Abstract] [PDF]
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 A. Vogiatzoglou, A. Oulhaj, A. D. Smith, E. Nurk, C. A. Drevon, P. M. Ueland, S. E. Vollset, G. S. Tell, and H. Refsum Determinants of Plasma Methylmalonic Acid in a Large Population: Implications for Assessment of Vitamin B12 Status Clin. Chem., December 1, 2009; 55(12): 2198 - 2206. [Abstract] [Full Text] [PDF]
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 D. S. Bhat, N. V. Thuse, H. G. Lubree, C. V. Joglekar, S. S. Naik, L. V. Ramdas, C. Johnston, H. Refsum, C. H. Fall, and C. S. Yajnik Increases in Plasma Holotranscobalamin Can Be Used to Assess Vitamin B-12 Absorption in Individuals with Low Plasma Vitamin B-12 J. Nutr., November 1, 2009; 139(11): 2119 - 2123. [Abstract] [Full Text] [PDF]
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 L M L de Lau, A D Smith, H Refsum, C Johnston, and M M B Breteler Plasma vitamin B12 status and cerebral white-matter lesions J. Neurol. Neurosurg. Psychiatry, February 1, 2009; 80(2): 149 - 157. [Abstract] [Full Text] [PDF]
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 R. M Winkels, I. A Brouwer, R. Clarke, M. B Katan, and P. Verhoef Bread cofortified with folic acid and vitamin B-12 improves the folate and vitamin B-12 status of healthy older people: a randomized controlled trial Am. J. Clinical Nutrition, August 1, 2008; 88(2): 348 - 355. [Abstract] [Full Text] [PDF]
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G. Hay, C. Johnston, A. Whitelaw, K. Trygg, and H. Refsum Folate and cobalamin status in relation to breastfeeding and weaning in healthy infants Am. J. Clinical Nutrition, July 1, 2008; 88(1): 105 - 114. [Abstract] [Full Text] [PDF]
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M. G. Garrod, R. Green, L. H. Allen, D. M. Mungas, W. J. Jagust, M. N. Haan, and J. W. Miller Fraction of Total Plasma Vitamin B12 Bound to Transcobalamin Correlates with Cognitive Function in Elderly Latinos with Depressive Symptoms Clin. Chem., July 1, 2008; 54(7): 1210 - 1217. [Abstract] [Full Text] [PDF]
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C. McCracken, P. Hudson, R. Ellis, A. McCaddon, and the Medical Research Council Cognitive Function an Methylmalonic acid and cognitive function in the Medical Research Council Cognitive Function and Ageing Study Am. J. Clinical Nutrition, December 1, 2006; 84(6): 1406 - 1411. [Abstract] [Full Text] [PDF]
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