Huang et al. [22] measured urine volume within 2.5 h after participants administered 1000 mL of water at sea level in an effort to predict HAPE. They found that urine volume in subjects who developed acute mountain response was significantly lower than that in the control group. In addition, the urine volumes at 1, 1.5, 2, and 2.5 h after hydration and the total urine volume within 1.5, 2, and 2.5 h after hydration were negatively associated with AMS. They concluded that greater urine volume within 2.5 h after hydration at sea level was associated with milder symptoms of acute mountain sickness after ascending to high altitude. Therefore, urine volume after hydration might be a marker for acute mountain sickness.