Determination of method-specific reference intervals for vitamin B12 and its correlation with holotranscobalamin

We aimed to compare total serum vitamin B12 measurements across four immunoassay platforms, establish method-specific reference intervals, evaluate the clinical impact of a uniform deficiency cut-off, and assess associations between total vitamin B12 and holotranscobalamin (holoTC).

Residual serum samples from 220 apparently healthy adults undergoing routine health check-ups were analyzed. Total vitamin B12 was measured on Beckman, Abbott, Siemens, and Roche platforms. Beckman analyses used the updated Access Vitamin B12 II calibrator introduced in December 2024. Holotranscobalamin was measured on the Abbott system. Reference intervals were derived using non-parametric methods according to CLSI EP28-A3c guidelines. Method comparison was performed using Passing-Bablok regression and concordance correlation coefficients (CCC), and associations between total vitamin B12 and holoTC were assessed using Spearman correlation analysis.

Total vitamin B12 concentrations differed significantly across platforms, with moderate to good agreement (CCC: 0.81-0.91). Study-derived lower reference limits (LRLs) varied substantially between assays and differed from manufacturer-provided values, most prominently for the Beckman platform. Application of a fixed deficiency cut-off of 148 pmol/L resulted in marked method-dependent differences in deficiency classification. Correlations between total vitamin B12 and holoTC were low to moderate across analytical platforms.

Serum vitamin B12 results vary across platforms, causing method-dependent LRLs and inconsistent classification with uniform cut-offs, underscoring the need for method-specific interpretation and improved harmonization. Low-to-moderate correlations reflect that holoTC and total vitamin B12 represent different components of vitamin B12 status and that total vitamin B12 assays differ by platform in reflecting the active fraction.