Long-term stability of amino acids and acylcarnitines in dried blood spots.
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.
Strnadová
Kristina Anna
KA
Department of Paediatrics, 3rd Faculty of Medicine, Charles University, Prague, Czech Republic.
Holub
Margareta
M
Mühl
Adolf
A
Heinze
Georg
G
Ratschmann
Rene
R
Mascher
Hermann
H
Stöckler-Ipsiroglu
Sylvia
S
Waldhauser
Franz
F
Votava
Felix
F
Lebl
Jan
J
Bodamer
Olaf A
OA
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
D000596:Amino Acids; C116917:acylcarnitine; D002331:Carnitine