24-h Void number as an indicator of hydration status

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.Subjects/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 U OSM (457±180 versus 874±175 mOsm/kg H 2 O; 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.