RIA for Serum Holo-Transcobalamin: Method Evaluation in the Clinical Laboratory and Reference Interval

(holoTC) could be the earliest marker of cobalamin (Cbl) deficiency, but there has been no method suitable for routine use. We evaluated a new commercial holoTC RIA, determined reference values, and assessed holoTC concentrations in relation to other biochemical markers of Cbl deficiency. Methods: The reference population consisted of 303 individuals 22–88 years of age, without disease or med-ication affecting Cbl or homocysteine metabolism. In elderly individuals (>65 years), normal Cbl status was further confirmed by total homocysteine (tHcy; <19 mol/L) and methylmalonic acid (MMA; <0.28 mol/L) concentrations within established reference intervals. HoloTC in Cbl deficiency was studied in a population of 107 elderly individuals with normal renal function