Received on August 3, 2006
Accepted on January 8, 2007

Endocrinology and Metabolism

Endocrinology and Metabolism: Long-Term Stability of Amino Acids and Acylcarnitines in Dried Blood Spots

¹ Department of Paediatrics, 3rd Faculty of Medicine, Charles University, Prague, Czech Republic, and Department of General Pediatrics, University Children's Hospital Vienna, Vienna, Austria
² Department of General Pediatrics, University Children's Hospital Vienna, Vienna, Austria
³ Section of Clinical Biometrics, Core Unit for Medical Statistics and Informatics, Medical, University of Vienna, Vienna, Austria
⁴ Pharm-analyt Laboratory GmbH, Baden, Germany
⁵ Children's Hospital British Columbia University, Vancouver, British Columbia, Canada
⁶ Department of Paediatrics, 3rd Faculty of Medicine, Charles University, Prague, Czech Republic

^* To whom correspondence should be addressed. E-mail: olaf.bodamer{at}meduniwien.ac.at.

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.