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

¹ Neo Gen Screening, PO Box 219, Bridgeville, PA 15017

² Centers for Disease Control and Prevention, 4770 Buford Hwy. NE, Atlanta, GA
^a author for correspondence: fax 412-220-0784, e-mail dhchace@neogenscreening.com

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 specimens analyzed by MS-MS per year throughout the world, the demand is acute for assay standardization and harmonization. Programs exist at the CDC for amino acid standardization and quality assurance pertaining to newborn 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 extremely unusual result was observed for octanoylcarnitine: 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 prevented or accounted for. The results of this study demonstrate 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-²H₃-octanoylcarnitine, L-²H₉-myristoylcarnitine, and L-²H₃-palmitoylcarnitine) from Cambridge Isotope Laboratories. Unlabeled standards (D,L-octanoylcarnitine, D,L-myristoylcarnitine, and L-palmitoylcarnitine) were obtained from Sigma, and L-propionylcarnitine, L-butyrylcarnitine, and L-octanoylcarnitine were obtained from Life Sciences Resources. The unlabeled standards were used to prepare a series of blood specimens at the CDC using procedures described previously (3)(4) with the following . . . [Full Text of this Article]

References

The following articles in journals at HighWire Press have cited this article:

				D. H. Chace, J. C. DiPerna, T. A. Kalas, R. W. Johnson, and E. W. Naylor Rapid Diagnosis of Methylmalonic and Propionic Acidemias: Quantitative Tandem Mass Spectrometric Analysis of Propionylcarnitine in Filter-Paper Blood Specimens Obtained from Newborns Clin. Chem., November 1, 2001; 47(11): 2040 - 2044. [Full Text] [PDF]