Isotope-dilution assay for urinary methylmalonic acid in the diagnosis of vitamin B12 deficiency. A prospective clinical evaluation.
Journal Article (Journal Article)
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.
- Matchar, DB; Feussner, JR; Millington, DS; Wilkinson, RH; Watson, DJ; Gale, D
- May 1987
Volume / Issue
- 106 / 5
Start / End Page
- 707 - 710
International Standard Serial Number (ISSN)
Digital Object Identifier (DOI)
- United States