Automated analysis of free l-carnitine and total short-chain acylcarnitine

Disclosed is a method of assaying free L-carnitine and total short-chain acylcarnitine in blood. The method uses essentially protein-free samples of plasma or serum and comprises (a) obtaining a sample of ultrafiltrated plasma or serum, (b) converting essentially all carnitine to acetylcarnitine using an enzymatic reaction, (c) converting essentially all free coenzyme A liberated in the enzymatic reaction of (b) to thiophenylate, (d) evaluating the sample spectrophotometrically to determine the amount of thiophenylate present, (e) obtaining a fresh sample of ultrafiltrated plasma or serum and hydrolyzing the sample to convert essentially all short-chain acylcarnitine to carnitine, and (f) repeating steps (b) through (d). All steps following the ultrafiltration of the sample are carried out within a pre-programmed, automated centrifugal analyzer. The use of this method to measure only free L-carnitine or only total short-chain acylcarnitine in plasma or serum samples is also disclosed, as is a kit for carrying out the automated analysis of free L-carnitine and total short-chain acylcarnitine.