Sixty-one plasma samples from patients with inborn errors of fatty acid oxidation and from control subjects were analyzed in a blinded fashion for acylcarnitines by the radioisotopic exchange-high-performance liquid chromatographic method. All samples from patients with medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency (n = 30), some of which had been stored in a frozen state for several years, showed a prominent octanoylcarnitine peak. In all blood spots from 11 patients with MCAD deficiency, octanoylcarnitine was also detected. Control plasma specimens and blood spots contained small amounts of octanoylcarnitine; however, the octanoylcarnitine/acetylcarnitine ratio differentiated patients with MCAD deficiency. Longer-chain acylcarnitines were found in plasma of all three patients with defects in long-chain fatty acid oxidation. Plasma and blood spots from a patient with multiple acyl-coenzyme A dehydrogenase deficiency contained C4-acylcarnitine, hexanoylcarnitine, octanoylcarnitine, and decanoylcarnitine. The results suggest that the method may be highly sensitive in detecting MCAD deficiency and other defects in fatty acid oxidation from plasma or blood spots.
