What is measured: Ornithine (Orn), aspartic acid (Asp), glutamic acid (Glu), lysine (Lys), alanine acid (Ala), phenylalanine (Phe), isoleucine (Ile), leucine (Leu), proline (Pro), valine (Val), asparagine (Asn), glutamine (Gln), threonine (Thr), and tyrosine (Tyr).
Method(s): GC-MS/MS (1).
Free amino acids in plasma have been associated with risk of cancer, metabolic syndrome, diabetes and low levels are observed in frail, elderly persons (2). Branched chain amino acids (BCAA; Leu, Ile and Val) are associated with insulin resistance, diabetes type 2, cardiovascular disease and early kidney disease (2, 3), and the valine catabolites, 3-hydroxyisobutyrate (3HIB) is belived to play a key role in the development of insulin resistance (3).
Patient/subject: Prandial status affects concentration, which increases slightly after a protein rich meal.
Matrix: Serum or EDTA plasma.
Volume: Minimum volume is 50 µL, but 200 µL is optimal and allows reanalysis.
Preparation and stability: Most amino acids are stable.
Reported values: Orn: 30-90 µmol/L; Asp: 0-26 µmol/L; Glu: 20-140 µmol/L; Lys: 120-290 µmol/L; Ala: 230-510 µmol/L; Phe: 26-85 µmol/L; Ile: 40-140 µmol/L; Leu: 70-170 µmol/L; Pro: 110-360 µmol/L; Val: 150-350 µmol/L; Asn: 20-130 µmol/L; Gln: 390-700 µmol/L; Thr: 70-240 µmol/L; Tyr: 40-110 µmol/L.
Intraclass correlation coefficient (ICC): na.
1. Midttun, Ø., McCann, A., Aarseth, O., Krokeide, M., Kvalheim, G., Meyer, K., and Ueland, P.M. (2016). Combined measurement of 6 fat-soluble vitamins and 26 water-soluble functional vitamin markers and amino acids in 50 μL of serum or plasma by high-throughput mass spectrometry. Anal Chem 88, 10427-436.
2. Nagao, K., & Kimura, T. (2020). Use of plasma-free amino acids as biomarkers for detecting and predicting disease risk. Nutr Rev, 78(12 Suppl 2), 79-85.
3. Arany, Z., and Neinast, M. (2018). Branched chain amino acids in metabolic disease. Curr Diab Rep 18, 76.