Hew-Butler Tamara D, Eskin Christopher, Bickham Jordan, Rusnak Mario, VanderMeulen Melissa
Department of Human Movement Science, Exercise Science Program, Oakland University, Rochester, Michigan, USA.
BMJ Open Sport Exerc Med. 2018 Feb 1;4(1):e000297. doi: 10.1136/bmjsem-2017-000297. eCollection 2018.
Clinical medicine defines dehydration using blood markers that confirm hypertonicity (serum sodium concentration ([Na])>145 mmol/L) and intracellular dehydration. Sports medicine equates dehydration with a concentrated urine as defined by any urine osmolality (UOsm) ≥700 mOsmol/kgHO or urine specific gravity (USG) ≥1.020.
To compare blood versus urine indices of dehydration in a cohort of athletes undergoing routine screenings.
318 collegiate athletes (193 female) provided blood and urine samples and asked to rate how thirsty they were on a 10-point visual analogue scale. Serum was analysed for [Na], while serum and UOsm were measured using an osmometer. USG was measured using a Chemstrip. Data were categorised into dehydrated versus hydrated groupings based on these UOsm and USG thresholds.
Using UOsm ≥700 mOsmol/kgHO to define dehydration, 55% of athletes were classified as dehydrated. Using any USG ≥1.020 to define dehydration, 27% of these same athletes were classified as dehydrated. No athlete met the clinical definition for dehydration (hypertonicity; serum [Na]>145 mmol/L). Normonatremia (serum [Na] between 135 mmol/L and 145 mmol/L) was maintained in 99.7% of athletes despite wide variation in UOsm (110-1298 mOsmol/kgHO). A significant correlation was confirmed between serum [Na] versus UOsm (r=0.18; P<0.01), although urine concentration extremes did not reflect derangement in serum markers or thirst rating.
Urine concentration thresholds classified 27%-55% of collegiate athletes as dehydrated, while no athlete was dehydrated according to blood [Na] measurement. Practitioners should caution against using urine indices to diagnose or monitor dehydration, because urinary output is a response rather than a reflection of (tightly regulated) blood tonicity.
临床医学通过确认高渗性（血清钠浓度([Na])>145 mmol/L）和细胞内脱水的血液标志物来定义脱水。运动医学将脱水等同于由任何尿渗透压（UOsm）≥700 mOsmol/kgH₂O或尿比重（USG）≥1.020所定义的浓缩尿。
比较一组接受常规筛查的运动员的血液与尿液脱水指标。
318名大学生运动员（193名女性）提供血液和尿液样本，并要求他们在10分视觉模拟量表上对自己的口渴程度进行评分。分析血清中的[Na]，同时使用渗透压计测量血清和UOsm。使用化学试纸条测量USG。根据这些UOsm和USG阈值将数据分为脱水组和水合组。
使用UOsm≥700 mOsmol/kgH₂O来定义脱水，55%的运动员被归类为脱水。使用任何USG≥1.020来定义脱水，这些相同运动员中有27%被归类为脱水。没有运动员符合脱水的临床定义（高渗性；血清[Na]>145 mmol/L）。尽管UOsm差异很大（110 - 1298 mOsmol/kgH₂O），99.7%的运动员维持了正常血钠浓度（血清[Na]在135 mmol/L至145 mmol/L之间）。血清[Na]与UOsm之间确认存在显著相关性（r = 0.18；P<0.01），尽管尿液浓度极值并未反映血清标志物的紊乱或口渴评分。
尿液浓度阈值将27%至55%的大学生运动员归类为脱水，而根据血液[Na]测量没有运动员脱水。从业者应谨慎使用尿液指标来诊断或监测脱水，因为尿量是一种反应而非（严格调节的）血液张力的反映。
