Errors Caused by the Use of D,L-Octanoylcarnitine for

The use of tandem mass spectrometry (MS-MS) in the analysis of filter paper blood spots from newborns for acylcarnitines and amino acids has expanded significantly in recent years (1, 2). With estimates of 1 million speci-mens analyzed by MS-MS per year throughout the world, the demand is acute for assay standardization and har-monization. Programs exist at the CDC for amino acid standardization and quality assurance pertaining to new-born screening (3, 4). This program is being extended to include acylcarnitines, and the data in this report stem from that extension. Five metabolites are key in the diagnosis of several disorders of fat and organic acid metabolism. Preliminary results demonstrated excellent linearity for each of the five acylcarnitines added to blood. However, an ex-tremely unusual result was observed for octanoylcarni-tine: the recovery of octanoylcarnitine was significantly lower than that of other acylcarnitines. This observation is supported by Turner and Dalton (5), who report a 40% loss of octanoylcarnitine after addition to whole blood and plasma. We investigated the cause of this loss of octanoylcarnitine so that this serious error could be pre-vented or accounted for. The results of this study demon-strate the importance of assay standardization and the validation required in clinical screening that goes well beyond this particular quality-assurance/quality-control program for acylcarnitines. We obtained isotope-labeled internal standards (l-2H3-propionylcarnitine, l-2H3-butyrylcarnitine, l