Certainly, we know that voluntary body mass loss reduction (via reduction in extracellular fluid) continues to be a habitual practice in Olympic combat sports. This practice carries an increased risk of adverse health-related effects, particularly for the adolescent combat athletes. Unfortunately, the data the acute assessment of hydration status remains equivocal. Currently, there is on-going debate within the combat sport community on how best to measure whole-body fluid changes (e.g, hypohydration) which regularly occur in these athletes. Importantly, the inconsistency of research findings on measurement resolution of urinary readings may preclude a conclusive position stand within current combat sports research. Therefore, the aim of the present study was to determine the measurement resolution of multiple non-invasive diagnostic tools in real-life settings on a day-to-day basis. Furthermore, this study also investigated the prevalence of hypohydration and the association between urinary indices of hydration status and other presumably confounding factors (e.g., urine protein content, increased muscle mass, food and fluid intake) in elite youth boxers during their weight-stable phase before competition. Sixty-nine urine samples were collected over three days from 23 elite European adolescent boxers (17.3±1.9 years of age, 1 .75 ±0.08 m in height, 66.8±11.8 kg in body mass, 8.3±2.3 % of body mass expressed as fat, 7.1±0.9 years of boxing experience) and analysed by field and laboratory measures reflecting on hydration status. Data collection took place during a mutual international training camp, prior to a major competition. Overall macronutrient and water intake were assessed using dietary records. According to their anthropometric characteristics, boxers were stratified into two groups: light-weight boxers (Lwb) and heavy-weight boxers (Hwb). The effects on all dependent variables between experimental protocols were analysed using repeated measures ANOVA to detect any systematic biases between items For post hoc analysis Bonferroni’s test was adopted for multiple comparisons of dependent variables. The results demonstrated urine specific gravity (USG) and urine osmolality (UOSM) inconsistency (ICC range=0.38–0.52) for Lwb and Hwb boxers, respectively) during their weight-stable period and regardless of the ad libitum fluid intake (~3.0 L• day-1). Post-hoc test demonstrated no differences between time trials (F=3.02; p=0.09, η2=0.23), while for Hwb there was a significant difference only between trials 1 and 3 as USG increased by 0.5±0.4 % (F=8.90, η2=0.49; β=0.94; p<0.001). The UOSM readings showed significant time effect for both groups (F=13.32; p<0.001; β=0.99; 67 η2=0.39), while there was no group (F=0.08, p=0.93) or interaction effect (F=1.19, p=0.29). In Figure 2 post-hoc test showed differences in both Lwb and Hwb boxers over the course of the study, as UOSM increased between trial 1 i 3 by 11.2±12.8 % (F=5.17; p=0.01, β=0.79, η2=0.32) and 19.9±22.7 % (F=10.2; p=0.001, β=0.98, η2=0.48, respectively). High positive correlation between urinary dehydration markers were observed (r=0.88, p<0.001); these correlations were supported by tight Bland-Altman limits of agreement (-0.92 to 0.93). The variations observed in Bland-Altman plots between both urinary indices and total body water (TBW) (i.e. the ordinate) were greater than three standard deviations. The area under curve (AUC) demonstrated similar outcomes for both urinary indices (0.93, p<0.001) with high sensitivity (93.5%) and specificity (87.5%). Sixty-five percent of adolescent boxers were severely hypohydrated in spite of being in their weight stability period. Hypohydration was universally prevalent among all athletes on both test days with USG=1.028±0.003 g•mL-1, UOSM =1036±158 mOsmol•kg-1. A trivial association between mean of both urinary values and mean water content was observed (r=0.06; p=0.45; r=- 013, p=0.53), whilst TPC was not associated with any urinary dehydration markers (USG, p=0.27; UOSM, p=0.61), indicating that the inter-assay reliability of urine sampling may remain skewed, especially for samples which have increased protein content. The present outcomes find that the most prevalent urinary dehydration markers used to classify hydration status in competition exhibit large variability, and may be influenced by external factors like intense exercise, or others, resulting in increased false-positive findings, even during the weight-stable periods of real-life competition settings. It seems that the consistency of both urinary dehydration marker readings in combat athletes depends upon research design, experimental approach (e.g., laboratory conditions vs real-life settings) in particular. In opposite to the prevailing theory, urine osmolality should not be considered a gold standard dehydration index. In conclusion, this study implies that the physiological mechanisms underlying diagnostic accuracy of the most common non-invasive hydration markers requires further investigation to validate the measures in elite adolescent boxers. Albeit, there are several critical physiological and medical reasons for the mandatory hydration evaluation of adolescent boxers throughout their season, including body development, endocrine responses, cardiovascular risk factors.