Abstract
Residual newborn screening dried blood spots (DBS) are a valuable resource for research in the retrospective diagnosis of inborn errors of metabolism and biomarker analysis. Many metabolites are subject to degradation depending on time and storage conditions, such as temperature and humidity. We studied the stability of 15 amino acids (AAs) in dried blood spots stored in a refrigerator after newborn screening. Methods: We retrospectively analyzed the levels of 15 AAs in 248 residual DBS from the Kazakhstan neonatal screening program using tandem mass spectrometry. DBS were stored at 4°C and 55-70% humidity and randomly selected during 2019-2022. Amino acid stability was assessed using linear regression and estimating the decrease in concentration of each metabolite during each year. Results: Retrospective analysis of dried blood spot samples stored for one to four years showed that the decrease in concentrations of 15 AA occurred in order from most stable to least stable: valine, proline, isoleucine, leucine, tyrosine, phenylalanine, alanine, arginine, hydroxyproline, methionine, citrulline, glutamate, ornithine, glycine, and glutamine. Alanine, arginine, hydroxyproline, glycine, and glutamate decayed in line with linear regression. Conclusion: Storing dried blood spots at 4°C and 55-70% humidity is not optimal for amino acid stability. Data obtained from measuring amino acid levels in dried blood spots stored over time should be corrected to reduce the incidence of negative and false positive results.