title: Assessment of extracellular dehydration using saliva osmolality.
abstract: BACKGROUND
  When substantial solute losses accompany body water an isotonic hypovolemia (extracellular dehydration) results. The potential for using blood or urine to assess extracellular dehydration is generally poor, but saliva is not a simple ultra-filtrate of plasma and the autonomic regulation of salivary gland function suggests the possibility that saliva osmolality (Sosm) may afford detection of extracellular dehydration via the influence of volume-mediated factors.
  
  
  OBJECTIVE
  This study aimed to evaluate the assessment of extracellular dehydration using Sosm. In addition, two common saliva collection methods and their effects on Sosm were compared.
  
  
  METHODS
  Blood, urine, and saliva samples were collected in 24 healthy volunteers during paired euhydration and dehydration trials. Furosemide administration and 12 h fluid restriction were used to produce extracellular dehydration. Expectoration and salivette collection methods were compared in a separate group of eight euhydrated volunteers. All comparisons were made using paired t-tests. The diagnostic potential of body fluids was additionally evaluated.
  
  
  RESULTS
  Dehydration (3.1 ± 0.5% loss of body mass) decreased PV (-0.49 ± 0.12 L; -15.12 ± 3.94% change), but Sosm changes were marginal (<10 mmol/kg) and weakly correlated with changes in absolute or relative PV losses. Overall diagnostic accuracy was poor (AUC = 0.77-0.78) for all body fluids evaluated. Strong agreement was observed between Sosm methods (Expectoration: 61 ± 10 mmol/kg, Salivette: 61 ± 8 mmol/kg, p > 0.05).
  
  
  CONCLUSIONS
  Extracelluar dehydration was not detectable using plasma, urine, or saliva measures. Salivette and expectoration sampling methods produced similar, consistent results for Sosm, suggesting no methodological influence on Sosm.
authors.affiliation: Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Kansas St, Building 42, Natick, MA, 01760, USA.
authors.forename: Brett R
authors.initials: BR
authors.lastname: Ely
authors.forename: Samuel N
authors.initials: SN
authors.lastname: Cheuvront
authors.forename: Robert W
authors.initials: RW
authors.lastname: Kenefick
authors.forename: Marissa G
authors.initials: MG
authors.lastname: Spitz
authors.forename: Kristen R
authors.initials: KR
authors.lastname: Heavens
authors.forename: Neil P
authors.initials: NP
authors.lastname: Walsh
authors.forename: Michael N
authors.initials: MN
authors.lastname: Sawka
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D003681:Dehydration / Q000097:blood / Q000175:diagnosis* / Q000652:urine; D005260:Female; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D012463:Saliva / Q000737:chemistry*