Comparability and stability of holotranscobalamin levels in capillary and venous blood

Abstract Introduction Self-collected capillary blood has numerous advantages over venous samples taken via phlebotomy, as such the use of this finger-prick testing has increased over recent years, driven in some part by Covid antibody testing. However, there is limited evidence that venous and capillary serum is comparable for many routine analytes. In this study we aimed to determine whether capillary sampling could offer an alternative sampling method to venous for the assessment of vitamin B12 in the form of holotranscobalamin, and if this analyte was stable in unspun capillary blood for three days, thus allowing for samples to be returned by the postal system. Methods Matched pairs of capillary and venous blood samples were collected from 25 patients for the determination of holotranscobalamin, one set being processed on day zero, the other set being stored at ambient temperature and then processed on day three to mimic postal samples. Self-collected capillary blood was compared with phlebotomist-collected venous samples using correlation, Passing-Bablock regression, and Altman-Bland analysis. Results Passing-Bablock and Bland-Altman analysis showed holotranscobalamin levels in capillary and venous serum to be comparable and that the analyte was stable in unspun blood for at least three days at ambient temperatures. Conclusions We believe this is the first published study to determine if capillary blood sampling is an acceptable alternative to venous sampling for determining holotranscobalamin concentration; our data indicates that there is no significant difference in results from unspun venous and capillary blood stored at room temperature for at least 3 days compared to venous blood tested on the same day of collection.