Isotope-dilution assay for urinary methylmalonic acid in the diagnosis of vitamin B12 deficiency. A prospective clinical evaluation.

Abstract

Vitamin B12 deficiency is a frequently considered diagnosis for which there is no single, commonly available and accurate test. A urinary methylmalonic acid assay using gas chromatography-mass spectrometry has been proposed as the preferred test. We reviewed vitamin B12 assays on 1599 consecutive patients and prospectively studied all patients with low serum B12 levels (n = 75) and a random sample of patients with normal levels (n = 68). Of 96 evaluable patients, 7 had clinical deficiency. All 7 deficient patients had urinary methylmalonic acid levels greater than 5 micrograms/mg creatine (sensitivity, 100%; confidence interval, 65% to 100%). Of the 89 patients who were not clinically deficient, 88 had urinary methylmalonic acid levels less than or equal to 5 micrograms/mg creatinine (specificity, 99%). The overall test accuracy in this population was 99%. If the high sensitivity and specificity of the gas chromatography-mass spectrometry assay for urinary methylmalonic acid is supported by other clinical studies, the methylmalonic acid assay may become the reference standard for the diagnosis of vitamin B12 deficiency.

• Authors: D B Matchar, J R Feussner, D S Millington, R H Wilkinson Jr, D J Watson, D Gale
• Journal: Annals of internal medicine (Ann Intern Med) Vol. 106 Issue 5 Pg. 707-10 (May 1987) ISSN: 0003-4819 [Print] United States
• PMID: 3551712 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Malonates
• Methylmalonic Acid
• Deuterium
• Vitamin B 12

Topics

• Aged
• Deuterium
• Female
• Gas Chromatography-Mass Spectrometry
• Humans
• Indicator Dilution Techniques
• Male
• Malonates (urine)
• Methylmalonic Acid (urine)
• Middle Aged
• Predictive Value of Tests
• Prospective Studies
• Vitamin B 12 (blood)
• Vitamin B 12 Deficiency (diagnosis, urine)