First morning urine (FMU) assessment would be a practical and convenient solution for clinically acceptable detection of underhydration prior to competition/training, and for the general public. Thus, we thus sought to determine the diagnostic accuracy of FMU as a valid indicator of recent (previous 24 hr, 5 days average) hydration practices. For 5 consecutive days and one final morning, 67 healthy women (n = 38) and men (n = 29; age: 20 [1] years, body mass index: 25.9 [5.5]) completed 24-hr diet logs for total water intake (from beverages and foods, absolute and relative to body mass), 24-hr urine and FMU collection (last morning only) for osmolality (Osm), specific gravity (SG), and color (Col), and morning blood sampling for plasma osmolality and copeptin. Correlations determined significance and relationship strength among FMU and all other variables. Area under the receiver operating characteristic curves, sensitivity, specificity, and positive likelihood ratios were employed using previously reported values to indicate underhydration (total water intake < 30 ml/kg, osmolality > 500, and >800 mOsm/kg, specific gravity > 1.017, and copeptin > 6.93 pmol/L). FMU_Osm and FMU_SG were significantly correlated (p < .05) to all variables except the previous 5-day plasma osmolality. FMU_Col was only significantly correlated with other color time intervals and total water intake per gram. FMU_Osm held greatest utility (area under the receiver operating characteristic curve, sensitivity, and specificity >80%) overall, with the best outcome being FMU_Osm indicating a previous 24-hr osmolality threshold of 500 mOsm/kg (FMU_Osm criterion >710 mOsm/kg and positive likelihood ratio = 5.9). With less effort and cost restriction, FMU is a viable metric to assess underhydration.

晨尿 (FMU) 评估将是一种实用且方便的解决方案，可用于在比赛/训练之前以及对公众进行临床上可接受的水分不足检测。因此，我们试图确定 FMU 的诊断准确性，作为近期（前 24 小时，5 天平均）水合实践的有效指标。连续 5 天和最后一个早晨，67 名健康女性 ( n  = 38) 和男性 ( n  = 29；年龄：20 [1] 岁，体重指数：25.9 [5.5]) 完成了 24 小时总水饮食日志摄入量（来自饮料和食物，绝对量和相对于体重的量）、24 小时尿液和 FMU 采集（仅限前一天早上）以了解渗透压 (Osm)、比重 (SG) 和颜色 (Col)，以及晨间血液采样血浆渗透压和和肽素。相关性决定了 FMU 和所有其他变量之间的重要性和关系强度。接受者操作特征曲线下面积、灵敏度、特异性和阳性似然比均采用先前报告的值来指示水合不足（总水摄入量 < 30 ml/kg，渗透压 > 500 和 > 800 mOsm/kg，比重 > 1.017 ，和肽素 > 6.93 pmol/L)。 FMU_Osm 和 FMU_SG 与除前 5 天血浆渗透压之外的所有变量均显着相关 ( p < .05)。FMU_Col 仅与其他颜色时间间隔和每克总水摄入量显着相关。总体而言，FMU_Osm 具有最大的效用（接受者操作特征曲线下的面积、灵敏度和特异性 >80%），最佳结果是 FMU_Osm，表明之前 24 小时渗透压阈值为 500 mOsm/kg（FMU_Osm 标准 >710 mOsm/kg）阳性似然比 = 5.9）。由于需要较少的精力和成本限制，FMU 是评估水分不足的可行指标。