Delayed Deproteinization Causes Methodological Errors in Amino Acid Levels in Plasma Stored at Room Temperature Or -20[Degrees]C (Report‪)‬

INTRODUCTION Plasma amino acid profiles are used in physiological, clinical (Yoneda et al., 2001), nutritional (Sarwar and Botting, 1993), and metabolic research. Significant progress has been made in amino acid analysis of physiological samples since the first commercial amino acid analyzer was introduced in 1958 (Spackman et al., 1958). Currently, automatic chromatographic equipment is widely used for amino acid analysis. The more than 40 amino acids in biological fluids can be assayed within 2 hours (Endo et al., 1992; Boucher et al., 1997). However, despite technical and theoretical developments, results still vary widely between laboratories. Several parameters can affect the results of amino acid assays, including sample collection, hemolysis or blood clotting, anticoagulants, degradation of protein due to endogenous proteolytic activity (Hulmues et al., 2004; Saleh et al., 2006), the method of deproteinization, and preservation (Parvy et al., 1991). Thus when analyzing plasma or serum amino acid concentrations, it is critical to collect, preserve, and store the sample using procedures that minimize amino acid changes.