Short-Term Stability of Amino acids and Acylcarnitines in the Dried Blood Spots Used to Screen Newborns for Metabolic Disorders

Abstract

Objective Tandem mass spectrometry is increasingly used in the Middle East in newborn screening for inborn errors of metabolism using dried blood spots. The sensitivity and specificity of this system for analyzing fatty and amino acids, screening for more than 40 metabolic conditions, is known. However, the short term stability of acylcarnitines and amino acids in dried blood spots in extreme heat and humid conditions is not well documented. We examined the short term effect of heat and humidity on the levels of 7 amino acids and 10 acylcarnitines used in newborn screening for inherited metabolic disorders. Methods Dried blood spots were exposed with humidity <30% to temperatures of 4℃, room temperature, 37° C, and 45℃, and also with humidity >70% at 37° C and 45℃. Amino acids and acylcarnitines in the dried blood spots were analyzed by tandem mass spectrometry. Results During the eight days of the study in high temperature and high humidity storage, most acylcarnitines and amino acids lost almost 50% of initial concentration. After eight days’ exposure at 37℃ and 45℃ with humidity >70%, methionine was determined to be the most sensitive, and phenylalanine and leucine were the least sensitive amino acids. At 37℃ with humidity >70% C6 was the most sensitive and free carnitine (C0) was the least sensitive acylcarnitine; at 45℃ with humidity >70% C16 was the most sensitive and C0 was the least sensitive. Conclusion Low humidity and low temperature conditions are required for transportation and storage of dried blood spots.