Abstract / Summary
Introduction: We designed a new indicator of cobalamin deficiency, a condition that sometimes can be difficult to diagnose. Materials and methods: The new indicator is a combination of the plasma concentrations of cobalamin (P-cobalamin) and methylmalonic acid (P-MMA) adjusted to an estimated glomerular filtration rate (eGFR) of 100 mL/min/1.73 m 2 , called P-MMA 100 . First, P-cobalamin and P-MMA 100 are transformed to a multiplum of their median in the population (MoM-values). Second, the indicator iB12 is calculated as log 10 [MoM(P-cobalamin)]/[MoM(P-MMA 100 )] and adjusted for age and sex. We studied some characteristics of iB12 with data from 83119 patients in primary health care, and compared it to the cB12 indicator calculated from P-cobalamin and P-MMA as devised by Fedosov et al. (Clin Chem Lab Med 2015; 53(8):1215-1225). The refineR software was used to classify patients as probably cobalamin sufficient and probably cobalamin insufficient, and for estimating reference limits. Results: Overall, the two indicators correlated closely. However, the iB12 indicator was more robust against systematic analytical changes than the cB12 indicator, and varied less with eGFR. For both indicators, a reasonably safe cut-off limit for cobalamin deficiency would be higher than their 2.5 percentile reference limit. Conclusion: The new iB12 indicator is an improvement of the corresponding cB12 indicator.