Methylmalonic Acid Excretion Studies

Summary. Oral valine and isoleucine were equally effective in producing an increased urinary excretion of methylmalonic acid (MMA) in vitamin B12 deficiency but oral MMA itself, methionine and leucine were unsatisfactory. MMA excretion was increased in 16 out of 23 patients with vitamin B12 deficiency after valine and/or isoleucine loading but remained normal in seven patients. These latter patients tended to have the highest serum vitamin B12 levels and were the least anaemic. Thus, normal MMA excretion cannot be used as evidence to exclude vitamin B12 deficiency. The excretion was within normal limits in patients with hepatic cirrhosis and in patients with folate deficiency.