Methylmalonic acid concentration in serum not affected in hepatic disease

Accumulation of methylmalonic acid may provide an early clue to deficiency of cobalamin (vitamin B12) in tissue. Metabolic abnormalities involving precursors of methylmalonic acid are frequently observed in patients with hepatic diseases. To establish whether methylmalonic acid accumulates and thereby gives false-positive test results for cobalamin deficiency, we measured the concentration of methylmalonic acid in serum of patients with various hepatic diseases. Many of the patients had increased concentrations of cobalamin in serum. In serum from 70 patients, the mean concentration of methylmalonic acid (252, SE 25 nmol/L) did not differ significantly from that found in healthy subjects (211, SE 12 nmol/L). We conclude that the assay of methylmalonic acid in serum may be useful for evaluating cobalamin status in hepatic disease with functional cobalamin deficiency despite an artificially increased normal or high concentration of cobalamin in serum.