title: Variability of measurements of sweat sodium using the regional absorbent-patch method.
abstract: BACKGROUND
  There is interest in including recommendations for the replacement of the sodium lost in sweat in individualized hydration plans for athletes.
  
  
  OBJECTIVE
  Although the regional absorbent-patch method provides a practical approach to measuring sweat sodium losses in field conditions, there is a need to understand the variability of estimates associated with this technique.
  
  
  METHODS
  Sweat samples were collected from the forearms, chest, scapula, and thigh of 12 cyclists during 2 standardized cycling time trials in the heat and 2 in temperate conditions. Single measure analysis of sodium concentration was conducted immediately by ion-selective electrodes (ISE). A subset of 30 samples was frozen for reanalysis of sodium concentration using ISE, flame photometry (FP), and conductivity (SC).
  
  
  RESULTS
  Sweat samples collected in hot conditions produced higher sweat sodium concentrations than those from the temperate environment (P = .0032). A significant difference (P = .0048) in estimates of sweat sodium concentration was evident when calculated from the forearm average (mean ± 95% CL; 64 ± 12 mmol/L) compared with using a 4-site equation (70 ± 12 mmol/L). There was a high correlation between the values produced using different analytical techniques (r2 = .95), but mean values were different between treatments (frozen FP, frozen SC > immediate ISE > frozen ISE; P < .0001).
  
  
  CONCLUSIONS
  Whole-body sweat sodium concentration estimates differed depending on the number of sites included in the calculation. Environmental testing conditions should be considered in the interpretation of results. The impact of sample freezing and subsequent analytical technique was small but statistically significant. Nevertheless, when undertaken using a standardized protocol, the regional absorbent-patch method appears to be a relatively robust field test.
authors.affiliation: Sports Nutrition, Australian Institute of Sport, Canberra, ACT, Australia.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Dziedzic
authors.forename: Megan L
authors.initials: ML
authors.lastname: Ross
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Slater
authors.forename: Louise M
authors.initials: LM
authors.lastname: Burke
mesh_terms: D000042:Absorption; D000328:Adult; D001642:Bicycling; D015415:Biomarkers / Q000378:metabolism; D004553:Electric Conductivity; D015444:Exercise; D006358:Hot Temperature; D006801:Humans; D017736:Ion-Selective Electrodes; D008297:Male; D008954:Models, Biological; D010783:Photometry; D015203:Reproducibility of Results; D012964:Sodium / Q000378:metabolism*; D013048:Specimen Handling / Q000295:instrumentation / Q000379:methods*; D013542:Sweat / Q000378:metabolism*; D013546:Sweating; D013997:Time Factors; D014882:Water-Electrolyte Balance; D055815:Young Adult
chemical_list: D015415:Biomarkers; D012964:Sodium