Three new tools to diagnose B12 deficiency: eGFR-adjusted methylmalonic acid (MMA ₁₀₀ ), a bivariate reference area for MMA ₁₀₀ and cobalamin, and a cobalamin deficiency index

, and studied the effect of different decision limits on the prevalence of positive test results in a patient population. Using the 2.5 percentile of CDI in the reference population as a decision limit gave a prevalence of 5.2% positive test results in the patient population. However, as a gold standard for cobalamin deficiency does not exist, we were unable to study the diagnostic accuracy of the CDI. Therefore, the true diagnostic accuracy of these tools is yet unknown and should be investigated.