Age-related variations in acylcarnitine and free carnitine concentrations measured by tandem mass spectrometry.

Background: The acylcarnitine profiles obtained from dried blood spots on "Guthrie cards" have been widely used for the diagnosis and follow-up of children suspected of carrying an inherited error of metabolism, but little attention has been paid to potential age-related variations in the reference values. In this study, we evaluated the variations in free carnitine and acylcarnitine concentrations with age, as measured by tandem mass spectrometry.

Methods: Filter-paper blood spots were collected from 433 healthy individuals over a period of 17 months. Eight age groups were defined: cord blood, 3-6 days (control group), 15-55 days, 2-18 months, 19-59 months, 5-10 years, 11-17 years, and 18-54 years. Free carnitine and acylcarnitines were measured for each individual. Mean values were calculated for each age group and compared with those for the control group.

Results: Free carnitine was significantly higher in older children than in newborns (P <0.05), but the concentrations of several acylcarnitines tended to be significantly lower in cord blood and in groups of older children than in the control group. Only minor sex-related differences were observed.

Conclusion: Although the risk of underdiagnosis of fatty acid oxidation disorders with the use of newborn values as reference can be considered as small, in some circumstances the use of age-related reference values may have a potential impact on the diagnosis and management of inherited errors of metabolism.