Stable-isotope selected-ion monitoring quantification of methylmalonic acid in dried filter-paper urine samples

Urea and creatinine were measured by Kodak Ektachem methods and methylmalonic acid by stable-isotope gas chromatography-mass spectrometry in 24 urine samples from patients with methylmalonic acidaemia. For each sample analyses were performed both directly on the liquid urine and on an aliquot which had been blotted onto filter paper and dried. There was good correlation between the methylmalonate/creatinine ratios in liquid and dried urine (r(2)=0.983). Urine dried on filter paper can be used advantageously for monitoring treatment in patients with this disorder.