Plasma cis-dec-4-enoic acid measured by isotope dilution mass spectrometry; an improved assay to diagnose medium-chain acyl-CoA dehydrogenase deficiency.

An isotope dilution mass spectrometric assay for plasma cis-dec-4-enoic acid is described. It is quicker, more reliable and more accurate than previous methods. It confirmed previous findings that cis-dec-4-enoic acid is a reliable indicator for medium-chain acyl-CoA dehydrogenase deficiency (MCAD). The plasma cis-dec-4-enoic acid levels of both asymptomatic and symptomatic MCAD patients (3.5-71 mumol/L) are demonstrably higher than those of normal children (0.2-1.7 mumol/L), MCAD heterozygotes (0.1-1.5 mumol/L), those with other fatty acid oxidation defects (0.2-2.2 mumol/L) or those receiving high doses of valproic acid (0.2-0.4 mumol/L).