Testing MMA ₁₀₀ – the eGFR-adjusted concentration of methylmalonic acid in plasma

The concentration of methylmalonic acid (MMA) in plasma increases in patients with cobalamin deficiency (CD). Independent of the cobalamin status, MMA also increases with decreasing glomerular filtration rate (GFR). Therefore, the physician who assesses MMA values must consider the patients' renal function. In order to avoid intuitive assessments, we have suggested that the laboratory should adjust MMA to an estimated GFR (eGFR) value of 100 mL/min/1.73 m². We named this measure MMA₁₀₀ (Åsberg et al.). Now, we used a large clinical data set to compare three characteristics of MMA₁₀₀ and MMA: The relation to eGFR, the diagnostic accuracy, and the upper reference limits for various age groups. In this material, MMA₁₀₀ was not totally unrelated to eGFR, but far less so than MMA. MMA₁₀₀ also had a higher diagnostic accuracy than MMA. The upper reference limits of MMA₁₀₀ varied less with age than those of MMA. In conclusion, MMA₁₀₀ was a better biomarker of CD than MMA.