Comparison of Amino Acid Concentrations in Plasma and Dried Blood Spot Samples Using LC-MS/MS

Background: Dried blood spot samples are suitable for diagnosing some congenital errors of metabolism; however, they provide limited benefit in the regular monitoring of amino acids. Objectives: The present study aimed to evaluate alanine (Ala), arginine (Arg), citrulline (Cit), glutamic acid (Glu), glycine (Gly), isoleucine (Ileu), leucine (Leu), methionine (Met), ornithine (Orn), phenylalanine (Phe), tyrosine (Tyr), and valine (Val) amino acid concentrations in dried blood and plasma samples obtained simultaneously. Methods: Amino acid concentrations were determined in the plasma, and dried blood spot samples obtained simultaneously from 145 patients (50 females and 95 males). Amino acid concentrations in the plasma and dried blood spot samples were studied by LC-MS/MS using original kits. Results: There were significant differences between dried blood spots and plasma in all amino acid concentrations, except for Met and Val. Bland-Altman analysis revealed the highest mean differences in Glu (-148.1), Gly (-70.1), and Ala (-58.1). Deming regression analysis showed that plasma and dried blood spot samples were consistent concerning Cit, Met, Phe, and Tyr concentrations. Conclusions: Differences in methodology and sample can influence amino acid concentrations. Dried blood spot samples might cause errors in amino acid screening programs.