Biological variation of holotranscobalamin and cobalamin in healthy individuals.

Data on biological variation for cobalamin and holotranscobalamin (holoTC) are limited. The aim of this study was to determine within-subject (CVI) and between-subject (CVG) biological variations for these analytes in a healthy population. We collected blood samples from 15 healthy volunteers (12 women and three men, 22-66 years) on the same weekday for 10 consecutive weeks. Serum samples were stored at -80 °C until analysis in duplicate in a single analytical run. The CVI and CVG were estimated by nested ANOVA. The CVI (95% CI) for cobalamin and holoTC was 6.7% (5.7-7.7) and 13.0% (11.5-15.0), respectively. The corresponding CVG was 24.1% (16.4-36.0) and 24.6% (16.3-37.7). The analytical variation (CVA) (95% CI) was 3.5% (3.2-4.0) for cobalamin and 2.4% (2.1-2.6) for holoTC. The index of individuality (II) was low (<0.6) for both cobalamin and holoTC and the reference change value (RCV) was 20.1% for cobalamin and 36.6% for holoTC. Our study describes the components of biological variation of cobalamin and holoTC in a healthy population, contributing to a better clinical interpretation of these biomarkers.