title: Implications of the variability in time to isotopic equilibrium in the deuterium dilution technique.
abstract: OBJECTIVE
  To investigate the variability in isotopic equilibrium time under field conditions, and the impact of this variability on estimates of total body water (TBW) and body composition.
  
  
  METHODS
  Following collection of a fasting baseline urine sample, 10 women and 10 men were dosed with deuterium oxide (0.05 g/kg body weight). Urine samples were collected every hour for 8 h. The samples were analysed using isotope ratio mass spectrometry. Time to equilibration was determined using three commonly employed data analysis approaches.
  
  
  RESULTS
  Isotopic equilibrium was reached by 50, 80 and 100% of participants at 4, 6 and 8 h, respectively. The mean group equilibration determined using the three different plateau determination methods were 4.8+/-1.5, 3.8+/-0.8 and 4.9+/-1.4 h. Isotopic enrichment, TBW, and percent body fat estimates differed between early (3-5 h), but not later sampling times (5-8 h).
  
  
  CONCLUSIONS
  Although the three different plateau determination approaches resulted in differences in equilibration time, all suggest that sampling at 6 h or later will decrease the likelihood of error in body composition estimates resultant from incomplete isotopic equilibration in a small proportion of individuals.
authors.affiliation: School of Human Movement Studies, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia. r.colley@qut.edu.au
authors.forename: R C
authors.initials: RC
authors.lastname: Colley
authors.forename: N M
authors.initials: NM
authors.lastname: Byrne
authors.forename: A P
authors.initials: AP
authors.lastname: Hills
mesh_terms: D000328:Adult; D001823:Body Composition / Q000502:physiology*; D001834:Body Water / Q000378:metabolism*; D001835:Body Weight / Q000502:physiology; D003903:Deuterium / Q000652:urine; D017666:Deuterium Oxide; D005260:Female; D006801:Humans; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D011865:Radioisotope Dilution Technique / Q000592:standards*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D003903:Deuterium; D017666:Deuterium Oxide