Background: Plasma amino acid analysis is key to the diagnosis and monitoring of inherited disorders of amino acid synthesis, catabolism and transport. Ion exchange chromatography (IEC) is widely accepted as the gold standard method of analysis, but with the introduction of liquid chromatography tandem mass spectrometry (LC-MS/MS) and liquid chromatography mass spectrometry (LC-MS) methods, this should now be questioned.
Methods: The analytical performance of three commercially available reagent kits, Waters AccQ Tag™ ULTRA LC-MS, SpOtOn Amino Acids LC-MS/MS and Chromsystems MassChrom® Amino Acid Analysis LC-MS/MS, were evaluated and compared with Biochrom Physiological Amino Acids ion exchange chromatography. Correlation with IEC was assessed by Passing-Bablok regression, concordance correlation coefficients (CCC) and Bland-Altman analysis for 21 common amino acids. Calculation of the total error from imprecision and bias was also used to benchmark performance.
Results: The MassChrom® and SpOtOn kits demonstrated acceptable inter-batch imprecision (CV < 10%) and accuracy (mean bias < 10%), whereas the AccQ Tag™ ULTRA kit did not. Good correlation (CCC > 0.95) with Biochrom IEC was demonstrated for 10/21 analytes in both the MassChrom® and SpOtOn kits and 6/21 in the AccQ Tag™ ULTRA kit.
Conclusions: The LC-MS assay demonstrated variable analytical performance and correlated poorly with ion exchange chromatography. Both LC-MS/MS assays demonstrated comparable analytical performance and reasonable correlation with ion exchange chromatography. They also confer practical advantages which cannot be realized by ion exchange chromatography, superior specificity and significantly faster analysis time, suggesting that ion exchange chromatography should no longer be described as the gold standard method for plasma amino acid analysis.
Keywords: Mass spectrometry; inborn errors metabolism; laboratory methods.