title: 24-h Void number as an indicator of hydration status.
abstract: OBJECTIVE
  Few user-friendly hydration assessment techniques exist for the general population to use on a daily basis. The present study evaluated void number over 24 h as a potential hydration assessment tool.
  
  
  METHODS
  Male and female subjects collected urine for 24 h while adequately hydrated (n=44; 22 ± 4 years, 168 ± 16 cm, 73 ± 15 kg) or fluid restricted (n=43; 22 ± 3 years, 175 ± 10 cm, 81 ± 24 kg). As a control, participants were asked to void when feeling the 'first urge to void' on a commonly used urge scale and noted the volume of each void. For each sample, 24-h urine volume, osmolality (U(OSM)), specific gravity (U(SG)) and color were measured in the laboratory.
  
  
  RESULTS
  As designed, the level of urge upon voiding was consistent throughout the study (2 ± 0; 'first urge to void'). Samples were classified by U(SG) as either euhydrated (U(SG)<1.020) or hypohydrated (U(SG) ⩾ 1.020). Grouping by U(OSM) did not change results. Euhydrated versus hypohydrated individuals had greater 24-h urine volume (1933 ± 864 versus 967 ± 306 ml, respectively) and lower urine color (2 ± 1 versus 5 ± 1), U(SG) (1.012 ± 0.004 versus 1.025 ± 0.004) and UOSM (457 ± 180 versus 874 ± 175 mOsm/kg H2O; all P<0.001). Euhydrated individuals voided more than hypohydrated individuals over the 24-h period (5 ± 2 versus 3 ± 1 voids; P<0.001). Additionally, void number inversely correlated with hydration status as identified by U(SG) (r=-0.50; P<0.05) and U(OSM) (r=-0.56; P<0.05).
  
  
  CONCLUSIONS
  In conclusion, over 24 h, individuals with a higher void number were euhydrated (that is, had less concentrated hydration biomarkers) than those with a lower void number. Based on these data, void number might be utilized as a simple and feasible hydration assessment for the general public, as it utilizes no equipment or technical expertise.
authors.affiliation: Human Performance Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Burchfield
authors.affiliation: Human Performance Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Ganio
authors.affiliation: Human Performance Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Kavouras
authors.affiliation: Human Performance Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Adams
authors.affiliation: Human Performance Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Gonzalez
authors.affiliation: Human Performance Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, USA.
authors.forename: C B
authors.initials: CB
authors.lastname: Ridings
authors.affiliation: Human Performance Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, USA.
authors.forename: N E
authors.initials: NE
authors.lastname: Moyen
authors.affiliation: Human Performance Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Tucker
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D003681:Dehydration / Q000175:diagnosis* / Q000652:urine*; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D013046:Specific Gravity; D013997:Time Factors; D016482:Urinalysis / Q000379:methods*; D014556:Urine / Q000737:chemistry*; D014882:Water-Electrolyte Balance / Q000502:physiology*; D055815:Young Adult