title: Long-term stability of amino acids and acylcarnitines in dried blood spots.
abstract: BACKGROUND
  Dried blood filter cards, collected for newborn screening, are often stored for long periods of time. They may be suitable for the retrospective diagnosis of inborn errors of metabolism, but no data are currently available on the long-term stability of amino acids and acylcarnitine species.
  
  
  METHODS
  We analyzed amino acids and acylcarnitines by tandem mass spectrometry in 660 anonymous, randomly selected filter cards from 1989 through 2004. We assessed long-term stability of metabolites by linear regression and estimated annual decrease of concentration for each metabolite.
  
  
  RESULTS
  Concentrations of free carnitine increased by 7.6% per year during the first 5 years of storage and decreased by 1.4% per year thereafter. Alanine, arginine, leucine, methionine, and phenylalanine decreased by 6.5%, 3.3%, 3.1%, 7.3%, and 5.7% per year, respectively. Acetylcarnitine, propionylcarnitine, citrulline, glycine, and ornithine decreased by 18.5%, 27.4%, 8.1%, 14.7%, and 16.3% per year during the first 5 years, respectively; thereafter the decline was more gradual. Tyrosine decreased by 1.7% per year during the first 5 years and 7.9% per year thereafter. We could not analyze medium- and long-chain acylcarnitine species because of low physiological concentrations.
  
  
  CONCLUSIONS
  Estimation of the annual decrease of metabolites may allow for the retrospective diagnosis of inborn errors of metabolism in filter cards that have been stored for long periods of time.
authors.affiliation: Department of Paediatrics, 3rd Faculty of Medicine, Charles University, Prague, Czech Republic.
authors.forename: Kristina Anna
authors.initials: KA
authors.lastname: Strnadová
authors.forename: Margareta
authors.initials: M
authors.lastname: Holub
authors.forename: Adolf
authors.initials: A
authors.lastname: Mühl
authors.forename: Georg
authors.initials: G
authors.lastname: Heinze
authors.forename: Rene
authors.initials: R
authors.lastname: Ratschmann
authors.forename: Hermann
authors.initials: H
authors.lastname: Mascher
authors.forename: Sylvia
authors.initials: S
authors.lastname: Stöckler-Ipsiroglu
authors.forename: Franz
authors.initials: F
authors.lastname: Waldhauser
authors.forename: Felix
authors.initials: F
authors.lastname: Votava
authors.forename: Jan
authors.initials: J
authors.lastname: Lebl
authors.forename: Olaf A
authors.initials: OA
authors.lastname: Bodamer
mesh_terms: D000596:Amino Acids / Q000097:blood*; D001800:Blood Specimen Collection; D002331:Carnitine / Q000031:analogs & derivatives* / Q000097:blood; D006801:Humans; D007231:Infant, Newborn; D016014:Linear Models; D008661:Metabolism, Inborn Errors / Q000175:diagnosis; D008954:Models, Biological; D015997:Neonatal Screening / Q000379:methods*; D013997:Time Factors
chemical_list: D000596:Amino Acids; C116917:acylcarnitine; D002331:Carnitine