Screening elderly populations for cobalamin (vitamin B12) deficiency using the urinary methylmalonic acid assay by gas chromatography mass spectrometry

PURPOSE: This study assesses the value of the urinary methylmalonic acid (MMA) assay by gas chromatography mass spectrometry as a screening procedure for detection of cobalamin (Cbl) deficiency and estimates the prevalence of undetected Cbl deficiency in elderly populations. SUBJECTS AND METHODS: A total of 809 elderly individuals over age 65 were screened using random spot urine specimens from 4 different sites: a health fair, retirement apartments, a hospital-based elderly assessment center, and a nursing home. Follow-up tests included serum total Cbl, serum MMA, and normalization of urinary and serum MMA levels with Cbl intramuscular (IM) therapy. RESULTS: The prevalence of elevated urinary MMA varied across population groups, from 3.0% in elderly visiting a health fair to 5.1% in elderly residing in retirement apartments. Follow-up on 35 of 36 subjects with elevated urinary MMA levels showed that 18 had low serum total Cbl (less than 180 pg/mL at Hospital 1 or less than 200 pg/mL at Hospital 2), 12 had low-normal Cbl (180 or 200 pg/mL to 350 pg/mL), and 5 had normal Cbl. Of the 12 subjects with low-normal Cbl on retesting, further assessment was performed in 7, and all 7 of these subjects had evidence of Cbl deficiency. Cbl IM therapy was initiated for 23 subjects; 16 were seen for follow-up and all had normal urinary MMA. CONCLUSION: The relatively high prevalence of undetected Cbl deficiency identified in the seniors warrants additional studies of elderly populations. The sensitivity, convenience, and noninvasive nature of the urinary MMA assay by gas chromatography mass spectrometry make it a practical screening test.