Validity of combined hydration self-assessment measurements to estimate a low vs. high urine concentration in a small sample of (tactical) athletes.

PURPOSE: Relationships between body weight, urine color (Uc), and thirst level (WUT) have been proposed as a simple and inexpensive self-assessment method to predict dehydration. This study aimed to determine if this method also allowed us to accurately identify a low vs. high urine concentration in (tactical) athletes. METHODS: A total of n = 19 Army Reserve Officer Training Corps cadets and club sports athletes (22.7 ± 3.8 years old, of which 13 male) were included in the analysis, providing morning body weight, thirst sensation, and Uc for five consecutive days. Each item received a score 0 or 1, resulting in a WUT score ranging from 0 (likely hydrated) to 3 (very likely dehydrated). WUT model and individual item outcomes were then compared with a ≥ 1.020 urine specific gravity (USG) cut-off indicating a high urine concentration, using descriptive comparisons, generalized linear mixed models, and logistic regression (to calculate the area under the curve (AUC)). RESULTS: WUT score was not significantly predictive of urine concentration, z = 1.59, p = 0.11. The AUC ranged from 0.54 to 0.77 for test days, suggesting a fair AUC on most days. Only Uc was significantly related to urine concentration, z = 2.49, p = 0.01. The accuracy of the WUT model for correctly classifying urine samples with a high concentration was 68% vs. 51% of samples with a low concentration, resulting in an average accuracy of 61%. CONCLUSION: This study shows that WUT scores were not predictive of urine concentration, and the method did not substantially outperform the accuracy of Uc scoring alone.

Risk factors associated with indicators of dehydration among migrant farmworkers.

OBJECTIVE: Farmworkers are at increased risk of adverse health outcomes related to occupational heat exposure and inadequate access to water, shade, or rest breaks. Presently, there is a dearth of studies examining the prevalence of dehydration and related factors in U.S. farmworkers. Our objectives were to characterize hydration status during typical workdays and to identify risk factors associated with increased dehydration in migrant farmworkers employed in Florida. METHODS: Urine samples were collected and analyzed for urine specific gravity (USG) 2-3 times per person per day over five days in May 2021 and 2022. Data collection included demographic characteristics, wet-bulb-globe-temperature (WBGT), and information on working conditions (task type, duration, and crop units harvested), fluid intake, clothing worn, and heat safety behaviors. Multivariable mixed regression models were used to evaluate risk factors associated with change in USG levels (continuous) during a work shift. RESULTS: A total of 111 farmworkers participated in this study providing 1020 cumulative USG measurements, of which 96.8% of end-of-shift USG samples were above 1.020 indicating potential dehydration. In multivariable models, dehydration assessed using change in USG levels significantly declined with age (ß = -0.078; 95%CI: 0.150, -0.006) but showed significant increase with body mass index (ß = 0.016; 95%CI: 0.003, 0.028), WGBT (ß = 0.054; 95%CI:0.044, 0.064), mean shift duration, and state of primary residence. We did not find significant associations of dehydration with type of clothing worn, intake of employer-provided water, or crop units harvested during a shift in this sample of farmworkers. CONCLUSION: Our findings underscore the need for additional research to evaluate adverse outcomes related to dehydration and to better understand recovery patterns from chronic dehydration across workweeks and harvest seasons in migrant farmworkers.

Evaluation of protocols to determine urine output and urinary urea nitrogen excretion in dairy cows with and without dietary salt supplementation.

Urine output and urinary urea-N excretion (UUNe) excretion are critical measures to accurately evaluate N metabolism in lactating dairy cows and environmental concerns related to manure N. The objectives of this study were: (1) to compare estimates of UUNe, urine output, and related variables from 3 pre-established measurement protocols (bladder catheterization, external collection cup, and spot sampling) and from dietary salt supplementation, (2) to study temporal variation in UUNe, urine output, and related variables as affected by measurement protocol, and (3) to evaluate urine specific gravity as a predictor of urine output. Twelve multiparous Holstein cows were used in a split-plot, Latin square design. Cows were randomly assigned to a diet (main plot) containing either 0.7% or 1.6% NaCl (DM basis) and then assigned to a sequence of 3 protocols (subplot) in a balanced 3 × 3 Latin square with 14-d period. For each protocol, measurements were conducted every 4 h for 3 consecutive days. Urine output was determined gravimetrically for bladder catheterization and external collection cup or based on measured cow BW, measured urinary creatinine concentration, and the assumed creatinine excretion of 29 mg/kg BW per day for spot sampling. Urine specific gravity was measured by refractometry. When averaged over a 3-d measurement period and compared with bladder catheterization, spot sampling underestimated urine output (6.8 kg/d; 20%) and UUNe (26 g/d; 13%) but exhibited greater concentration of urinary urea-N (+58 mg/dL; 10%). There were no differences in any measurements determined via bladder catheterization or external cup device protocols, except for urine output that tended to be 3.7 kg/d lower for collection cup compared with bladder catheterization. The 2 gravimetric protocols yielded lower urinary creatinine concentration than spot sampling (64.7 vs. 88.1 mg/dL) and lower creatinine excretion (25.3 mg/kg BW per day) than the value of 29 mg/kg BW per day generally assumed in the spot sampling protocol. Salt supplementation tended to increase urine output (+5.2 kg/d) and decrease urinary urea-N concentration (-93 mg/dL), urinary creatinine concentration (-9.5 mg/dL), milk protein concentration (-0.19 percentage unit) and milk protein yield (-70 g/d). There was greater temporal variation of urine output when measured via the collection cup compared with bladder catheterization in the first 2 d but not the third day of sampling, suggesting that an extended period of adaptation might have improved data quality of the collection cup protocol. The R2 of the linear regression to predict urine output with urine specific gravity was 67%, 73%, and 32% for bladder catheterization, collection cup, and spot sampling, respectively. In this study, spot sampling underestimated both urine output and UUNe, but UUNe determination did not differ between external collection cup and bladder catheterization. However, our data suggested the need to investigate the adaptation protocol, required days of measurements and the conversion of urine mass to urine volume to improve accuracy and precision of urine collection protocols.

Bioelectrical Impedance Vector Analysis (BIVA) for Assessment of Hydration Status: A Comparison between Endurance and Strength University Athletes.

INTRODUCTION: Athletic performance is greatly impacted by hydration status. The combination of several techniques is recommended to accurately measure water losses and gains. AIM: The aim of this study is to assess the validity of bioelectrical impedance vector analysis (BIVA) as a tool for measuring hydration status in endurance and strength athletes. METHODS: A total of 148 athletes were evaluated on one experimental day, pre- and post-training. Urine samples were collected and analyzed for color and specific gravity. Body weight changes were measured, sweat rate was calculated, and BIVA was performed. Reference ellipses were plotted using data of 200 healthy non-athletic individuals. RESULTS: A moderate significant agreement was noted between raw bioelectrical values and urine specific gravity (USG) (p > 0.05). The sensitivity of classic BIVA in detecting minor changes in hydration status is confirmed both graphically and statistically. R/h and Z statistically significantly decreased post-training. Male athletes exhibited a specific BIA vector distribution compared to the reference population and were slightly more hydrated than female athletes. CONCLUSIONS: BIVA validation may be an essential step to allow its use among university students to assess dehydration in a non-invasive, practical, and inexpensive way.

Dehydration and Rapid Weight Gain Between Weigh-in and Competition in Judo Athletes: The Differences between Women and Men.

This study aimed to investigate the sex differences in short-term weight change and hydration status in judo athletes. Thirty-five men and 15 women judo athletes voluntarily participated in this descriptive and repeated measures design study. Body mass, urine-specific gravity (USG), and body composition of the athletes were measured at the official weigh-in and the competition day's morning. Body mass of the athletes increased during recovery time between official weigh-in and before the competition (time factor; F1-48 = 71.81, p < 0.001), this increase was higher in men athletes compared to women athletes (time-sex interaction; F1-48 = 6.56, p = 0.01). With RWG, USG values of the women and men athletes decreased (time factor; F1-48 = 8.53, p = 0.005). However, most of the athletes were still in significant or serious dehydration state. Unchanged values of total body water rates (TBW) supported dehydration in athletes before the competition (time factor, F1-48 = 2.9, p = 0.091; time-sex interaction; F1-48= 2.4, p = 0.122). The findings of the study indicated that RWG was higher in men athletes compared to women athletes, but hydration status was not affected by sex factor.Notwithstanding 15 hours of recovery between official weigh-in and the start of the competition, judo athletes were still in dehydrated state despite remaining within the limit set for RWG.

A lavatory urine color (LUC) chart method can identify hypohydration in a physically active population.

PURPOSE: To provide a new and efficient at-the-toilet-bowl method of self-assessing urine concentration via urine color (Uc) to identify hypohydration. METHODS: A large athletic population (n = 189) delivered a urine sample, then chose a color panel that was displayed on the back wall of the lavatory stall. Selection was based on duration of urine voiding time, so that for a short-duration, the lighter panel was selected; for a mid-duration, the mid color panel; and for a longer-void-duration, the darker panel was selected. Then, subjects noted if their urine was lighter than, similar to, or darker than the selected color panel. Trained investigators also rated subjects' urine samples. To assess validity of Uc classification, the outcome was compared with a urine concentration (urine specific gravity, USG, and urine osmolality) threshold indicating hypohydration. RESULTS: Urine color was scored similarly by subjects and investigators (P = 0.99). Based on receiver operating curves (ROC), the method scored fair, i.e., the area under the curve ranging 0.73-0.82, with an accuracy of participants and investigators correctly classifying 72% and 75% urine samples compared to a USG threshold of 1.020, respectively, and 62% and 70% compared to a urine osmolality threshold of 836 mmol·kg-1, respectively. CONCLUSION: This new lavatory urine color (LUC) method of scoring Uc levels to assess potential hypohydration gives results similar to those of traditional urine color charts, but it has the advantage of an immediate assessment of hydration status based on scoring urine color directly from the toilet bowl.

Associations between urinary hydration markers and metabolic dysfunction: a cross-sectional analysis of NHANES data, 2008-2010.

PURPOSE: Growing evidence suggests hydration plays a role in metabolic dysfunction, however data in humans are scarce. This study examined the cross-sectional association between hydration and metabolic dysfunction in a representative sample of the US population. METHODS: Data from 3961 adult NHANES (National Health and Nutrition Examination Survey) participants (49.8% female; age 46.3 ± 0.5 years) were grouped by quartile of urine specific gravity (USG, 2007-2008 cohort) or urine osmolality (UOsm, 2009-2010 cohort) as measures of hydration. Metabolic dysfunction was assessed by glycemic and insulinemic endpoints and by components of the metabolic syndrome. Multivariate-adjusted linear and logistic regression models were used. RESULTS: Increasing quartiles of USG but not UOsm was associated with higher fasting plasma glucose (FPG), glycated hemoglobin (all P < 0.01), HOMA-IR and elevated insulin (all P < 0.05). Compared with the lowest quartile, those with the highest USG but not UOsm had greater risk of metabolic syndrome (Q4 vs. Q1, OR (99% CI): 1.6 (1.0, 2.7), P = 0.01) and diabetes (Q4 vs. Q1, OR: 1.8 (1.0, 3.4), P < 0.05). Additionally, those with USG > 1.013 or UOsm > 500 mOsm/kg, common cut-off values for optimal hydration based on retrospective analyses of existing data, had less favorable metabolic markers. In a subset of participants free from diabetes mellitus, impaired kidney function, hypertension and diuretic medication, USG remained positively associated with FPG (P < 0.01) and elevated FPG (P < 0.05). CONCLUSION: These analyses provide population-based evidence that USG as a proxy for hydration is associated with glucose homeostasis in NHANES 2007-2008. The same association was not significant when UOsm was used as a proxy for hydration in the 2009-2010 wave. CLINICAL TRIAL REGISTRY: Not applicable, as this was a reanalysis of existing NHANES data.

Detection of voluntary dehydration in paediatric populations using non-invasive point-of-care saliva and urine testing.

AIM: Voluntary dehydration, or lack of fluid intake despite water availability, is common in otherwise healthy children, and can lead to adverse effects. Most dehydration biomarkers are impractical for routine assessment in paediatric populations. This study aimed to assess two non-invasive hydration assessment tools, urine specific gravity (USG ) and a novel point-of-care (POC) salivary osmolarity (SOSM) sensor, in healthy children. METHODS: Volunteers were tested by colorimetric USG and a handheld SOSM system. Observed values were compared against previous studies to determine hydration status, as was the concordance between parameters. RESULTS: At the common USG threshold of 1.020, 42.4% of the 139 healthy children were dehydrated. The same prevalence was found using the 70-mOSM cut-off value. Comparative analysis of SOSM at varying USG thresholds demonstrated significantly higher SOSM in dehydrated children with a USG  ≥ 1.030 (P = 0.002). CONCLUSION: At the USG threshold of 1.020 and SOSM threshold of 70 mOSM, 42.4% of healthy children were found to be voluntarily dehydrated. Significantly higher SOSM was observed in dehydrated children (USG ≥ 1.030). As the first study on the utility of POC SOSM measurements for detecting dehydration, these results provide a foundation for future POC characterisation of SOSM in other populations and clinical contexts.

Do initially non-dehydrated patients with acute ischemic stroke need fluid supplement?

Background: We previously found that dehydration is an independent predictor of early deterioration after acute ischemic stroke and rehydration helps to improve outcomes. There is limited evidence of how to treat patients who are initially non-dehydrated. In this study, we tested the hypothesis that rehydration therapy, based on the daily urine specific gravity, will improve the outcome of ischemic stroke patients who are initially non-dehydrated. Methods: We conducted a single-arm prospective study of patients with acute ischemic stroke with historical controls. For the first 5 days of study group, a daily urine specific gravity of > 1.020 g/ml was taken as indication for rehydration and patients were advised to drink water via oral or tubal feeding with a dose of 5 ml/kg body weight right away and after dinner. Control group patients were rehydrated without reference to urine specific gravity. An increase in National Institutes of Health Stroke Scale score of ≥ 4 within three days was defined as having stroke-in-evolution. Scores of ≤ 1 on the modified Rankin scale at 3 months were considered to indicate a favorable outcome. Results: A total of 125 patients were analyzed, 46 in the study group and 79 in the control group. The groups did not significantly differ in the stroke-in-evolution rate (4.3% vs. 8.2%, P = 0.474). The rate of favorable outcome at 3 months was significantly higher in the study group than in the control group (56.5% vs. 27.8%, P = 0.001). Conclusions: Urine specific gravity-based hydration might be a useful method to improve functional outcomes of patients with acute ischemic stroke who were non-dehydrated at admission.

Effects of Rapid Weight Loss on Kidney Function in Combat Sport Athletes.

Even though scientific literature shows numerous heath complications and performance decrements associated with rapid weight loss (RWL), its prevalence remains exceedingly high across various combat sports. The aim of this study was to thoroughly search the existing literature to explore the influence of RWL on kidney function in Olympic and non-Olympic combat sport athletes. PubMed and Web of Science were searched for the relevant studies. Only original articles published from 2005 onwards, written in English, that included healthy males and females who prompted ~5% weight loss within a week or less, were included in the study. Retrieved studies showed that creatinine, blood urea nitrogen and urine specific gravity values were significantly increased after RWL in the majority of the included studies. This observation indicates that RWL caused dehydration and subsequent acute kidney damage despite various degrees of weight lost during the RWL phase, which can lead to adverse events in other body systems. Alternative methods of weight reduction that prioritize athletes' health should be considered.