title: Reference intervals for plasma-free amino acid in a Japanese population.
abstract: BACKGROUND
  Plasma amino acid concentrations vary with various diseases. Although reference intervals are useful in daily clinical practice, no reference intervals have been reported for plasma amino acids in a large Japanese population.
  
  
  METHODS
  Reference individuals were selected from 7685 subjects examined with the Japanese Ningen Dock in 2008. A total of 1890 individuals were selected based on exclusion criteria, and the reference samples were selected after the outlier samples for each amino acid concentration were excluded. The lower limit of the reference intervals for the plasma amino acid concentrations was set at the 2.5th percentile and the upper limit at the 97.5th percentile.
  
  
  RESULTS
  By use of the nested analysis of variance, we analysed a large dataset of plasma samples and the effects of background factors (sex, age and body mass index [BMI]) on the plasma amino acid concentrations. Most amino acid concentrations were related to sex, especially those of branched-chained amino acid. The citrulline, glutamine, ornithine and lysine concentrations were related to age. The glutamate concentration was related to body mass index.
  
  
  CONCLUSIONS
  The concentrations of most amino acids are more strongly related to sex than to age or body mass index. Our results indicate that the reference intervals for plasma amino acid concentrations should be stratified by sex when the background factors of age and body mass index are considered.
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yamamoto
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Kondo
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tanaka
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan.
authors.forename: Takahiko
authors.initials: T
authors.lastname: Muramatsu
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan.
authors.forename: Hiroo
authors.initials: H
authors.lastname: Yoshida
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan akira_imaizumi@ajinomoto.com.
authors.forename: Akira
authors.initials: A
authors.lastname: Imaizumi
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Nagao
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Noguchi
authors.affiliation: Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Miyano
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000097:blood*; D005260:Female; D006801:Humans; D007564:Japan; D008297:Male; D008875:Middle Aged; D012016:Reference Values
chemical_list: D000596:Amino Acids
keywords: Mass spectrometry; chromatography