Lauroyl Chloride-d3 is an intermediate used in the synthesis of Lauroyl-d3-L-carnitine Hydrochloride (L178683), which is the labeled analogue of Lauroyl-L-carnitine Hydrochloride (L178680), a long-chain fatty ester of carnitine which is accumulated and released into the circulation, in fatty-acid oxidation defects. Pattern of Lauroyl-L-carnitine can be diagnostic for a number of ß-oxidation defects.