title: Age-related variations in acylcarnitine and free carnitine concentrations measured by tandem mass spectrometry.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Newborn Screening Center, Laboratory of Pediatrics, Free University of Brussels, Brussels, Belgium. catia.cavedon@gmail.com
authors.forename: Catia Testa
authors.initials: CT
authors.lastname: Cavedon
authors.forename: Pierre
authors.initials: P
authors.lastname: Bourdoux
authors.forename: Karl
authors.initials: K
authors.lastname: Mertens
authors.forename: Hong Vien
authors.initials: HV
authors.lastname: Van Thi
authors.forename: Nadine
authors.initials: N
authors.lastname: Herremans
authors.forename: Corinne
authors.initials: C
authors.lastname: de Laet
authors.forename: Philippe
authors.initials: P
authors.lastname: Goyens
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001800:Blood Specimen Collection; D002331:Carnitine / Q000031:analogs & derivatives* / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005312:Fetal Blood; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D008875:Middle Aged; D012016:Reference Values; D012737:Sex Factors
chemical_list: C116917:acylcarnitine; D002331:Carnitine