Measurement of Total Vitamin B12 and Holotranscobalamin, Singly and in Combination, in Screening for Metabolic Vitamin B12 Deficiency

• Published in: Clinical chemistry (Baltimore, Md.) Md.), 2006-02, Vol.52 (2), p.278-285
• Main Authors: Miller, J.W, Garrod, M.G, Rockwood, A.L, Kushnir, M.M, Allen, L.H, Haan, M.N, Green, R
• Format: Article
• Language: English
• Subjects: Aged; Aged, 80 and over; blood chemistry; blood plasma; California - epidemiology; Cohort Studies; disease diagnosis; elderly; Female; holotranscobalamin; homocysteine; Humans; Male; Mass Screening; methylmaloni acid; Middle Aged; transcobalamins; Transcobalamins - analysis; Vitamin B 12 - blood; Vitamin B 12 Deficiency - blood; Vitamin B 12 Deficiency - diagnosis; Vitamin B 12 Deficiency - epidemiology; vitamin B12; vitamin deficiencies
• ISSN: 1530-8561; 0009-9147; 1530-8561
• DOI: 10.1373/clinchem.2005.061382

Background: The standard screening test for vitamin B12 deficiency, measurement of total plasma vitamin B12, has limitations of sensitivity and specificity. Plasma vitamin B12 bound to transcobalamin (holoTC) is the fraction of total vitamin B12 available for tissue uptake and therefore has been proposed as a potentially useful alternative indicator of vitamin B12 status. Methods: We compared the diagnostic accuracy of total vitamin B12, holoTC, and a combination of both measures to screen for metabolic vitamin B12 deficiency in an elderly cohort (age >or= 60 years). Plasma methylmalonic acid and homocysteine were used as indicators of vitamin B12 deficiency. Results: Low total vitamin B12 (13 μmol/L) were observed in 12.1% and 17.0% of the study participants. In multiple regression models, holoTC explained 5%-6% more of the observed variance in methylmalonic acid and homocysteine than did total vitamin B12 (P