Biological variation of free plasma amino acids in healthy individuals

Abstract

Background: Biological variation data for free plasma amino acids are lacking from the more comprehensive databases. Therefore, we determined the intra-and inter-individual components of variation in healthy subjects. These data were used to define desirable goals for imprecision, bias and total error, indices of individuality and reference change values. Methods: Plasma samples were collected from 11 volunteers at weekly intervals over 5 weeks. Free plasma amino acids were analyzed by reversed-phase HPLC and analytical and biological variation data were derived using ANOVA. Results: Intra-individual coefficients of variation ranged from 9.5% to 46.4%, with lower values among the essential amino acids. The mean inter-individual coefficient of variation was 46.6% and was higher than intra-individual values for all amino acids. Thus, indices of individuality were below 0.8. Reference change values ranged from 30.9% to 128.4% and total error values ranged from 15.2% to 61.0%. Conclusions: Plasma amino acids exhibit relatively low intra-individual coefficients of variation, with essential amino acids showing tighter homeostatic control. Analytical quality goals can be reasonably achieved with current methods. Reference intervals are of limited value in the detection of unusual results in an individual. Therefore, comparison of serial results by means of the reference change values is recommended. Clin Chem Lab Med 2010;48:99-104.

Validation of an analytical method for human plasma free amino acids by high-performance liquid chromatography ionization mass spectrometry using automated precolumn derivatization

“…In our developed method, the repeatability was within 4.0%, the intermediate reproducibility was within 6.2%, and the reproducibility was within 7.0%. These results are within half of the biological variation of free plasma amino acids in healthy individuals for all amino acids [32].…”

“…Half of biological variation of free plasma amino acids in healthy individuals [32] High (spiked Std10) parallel processes can save approximately 8 min during the analysis cycle compared with the use of serial processes for the reaction and chromatographic separation steps. Furthermore, the UF-Amino Station system required no more than approximately 3 mL of washing water when compared with a previous home-built automated precolumn derivatization system using approximately 10 mL of washing water [25].…”

Acute tryptophan depletion reduces kynurenine levels: implications for treatment of impaired visuospatial memory performance in irritable bowel syndrome

“…However, within the healthy control group, total tryptophan levels (t(13)=2.35, p=0.036), and total kynurenine levels (t(13)= 3.96, p=0.002), were significantly higher prior to Trp− treatment than prior to Trp+ treatment (see Table 2). However, CV % for baseline, pre-treatment total tryptophan levels in IBS participants was 12.2 % and in healthy controls 13.2 %, and for baseline levels of total kynurenine levels in IBS was 10.7 % and in healthy controls 13.7 %, which are within the range of previously reported variations (Corte and Venta 2010).…”

“…In addition, pre-treatment levels of GI symptoms as measured by the IBS-SSS were analysed with univariate repeated measures ANOVA on each experimental session. In addition, a percentage coefficient of variance (CV %) was calculated for baseline levels of total tryptophan and total kynurenine for patients with IBS and healthy control participants to determine if variance between experimental days was within the normal range (Corte and Venta 2010).…”

Postprandial changes of amino acid and acylcarnitine concentrations in dried blood samples

“…These differences, such as age at blood collection, birth weight, or gestational age, could be overcome by age, birth weight, and gestational-age-related reference values. However, only few publications on these data exist, and they often take only the variation of a single variable into account (Cavedon et al 2005, Meyburg et al 2001, Chace et al 2003, Honzík et al 2005, Corte and Venta 2010, Duran 2008, Matern 2008. The influence of some medications, such as dopamine and steroids upon thyroid-stimulating hormone (TSH) (Wilber and Utiger 1969, Brabant et al 1989, Haugen 2009) and 17α-hydroxyprogesterone (17-OHP), respectively, is well known (Rohrer et al 2003).…”