Holotranscobalamin and Total Transcobalamin in Human Plasma: Determination, Determinants, and Reference Values in Healthy Adults

(MBAs) to identify determinants and to establish refer-ence 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 meth-ods. Determinants and reference values were deter-mined in 500 blood donors, ages 18–69 years. Results: Determination of cobalamin, holoTC, and TC by MBA required <150 L. 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 lowe