Quantitation of short- and medium-chain acylcarnitines in plasma by radioisotopic exchange/high-performance liquid chromatography.

A method for the quantitation of short- and medium-chain acylcarnitines in plasma and its clinical application are described. The method is based on enzymatic exchange of L-[3H]carnitine into the acylcarnitine pool, subsequent separation of labeled acylcarnitines by high-performance liquid chromatography, and quantitation of the radioactivity by a beta flowthrough detector. Since only acylcarnitines are detected, no sample cleanup procedure is required. Isotopic equilibrium, a prerequisite for accurate quantitation, was reached in plasma after 1 h of incubation for all acylcarnitines except isovalerylcarnitine which required a longer incubation time. No significant hydrolysis of acylcarnitines occurred during the incubation. Linearity was demonstrated after adding increasing amounts of individual acylcarnitines to plasma. The method is highly sensitive requiring no L-carnitine administration to the patient and differentiates short-chain acylcarnitine isomers. It is suitable for the detection of a number of inborn errors of organic acid and fatty acid metabolism.