Quantitation of urinary methylmalonic acid by gas chromatography mass spectrometry and its clinical applications

Urine methylmalonic acid (MMA) concentrations were detected in 79 Chinese patients by gas chromatography mass spectrometry (GC/MS), using a selected ion monitoring program. 10 of the 79 patients were found to have cobalamin deficiency. Their urine MMA amounts were all elevated with a mean value 1376 ng/μl (11.66 mmol/l), ranging from 40.46 to 3900 ng/μl (0.34-33.05 mmol/l). The remaining 69 cases were found to be unrelated to cobalamin deficiency. Their mean urine MMA was 3.62 ng/μl (30.0 μmol/l), ranging from 0–17.47 ng/μl (0–148.0 μmol/l). In this study, we found that urine MMA detected by GC/MS was a simple, rapid, convenient, specific and sensitive method for the diagnosis of cobalamin deficiency. The urine MMA concentrations in cases not due to cobalamin deficiency would not exceed 20 ng/μl (169.5 μmol/l), whereas in cobalamin deficiency the urine MMA levels always exceeded 20 ng/μl, or were even much higher. No overlapping of the results of urine MMA between these 2 groups of patients could be seen in our study. Detection of urine MMA is useful in the demonstration or exclusion of cobalamin deficiency in any suspect patients.