Detection of Vitamin B12 Deficiency in Older People by Measuring Vitamin B12 or the Active

creased vitamin B12 status have been associated with neurological and cognitive impairment. Current assays analyze total vitamin B12 concentration, only a small percentage of which is metabolically active. Concentra-tions of this active component, carried on holotransco-balamin (holoTC), may be of greater relevance than total vitamin B12. Methods: We compared the utility of serum holoTC with conventional vitamin B12 for detection of vitamin B12 deficiency in a population-based study of older people, using increased methylmalonic acid (MMA) concentrations as a marker of metabolic vitamin B12 deficiency in the overall population (n 2403) and in subsets with normal (n 1651) and abnormal (n 752) renal function