Hydration Marker Diagnostic Accuracy to Identify Mild Intracellular and Extracellular Dehydration

Area of Science:

• Exercise Physiology
• Human Performance
• Sports Medicine

Background:

• Mild dehydration, defined as ≤2% body mass loss, negatively impacts health and performance.
• Accurate identification of mild intracellular dehydration (ID) and extracellular dehydration (ED) is essential.
• The diagnostic accuracy of a single hydration marker for both ID and ED remains unclear.

Purpose of the Study:

• To determine the diagnostic accuracy of 15 hydration markers for identifying mild ID and ED.
• To assess if a single marker can reliably detect both types of mild dehydration.
• To evaluate the thirst 0-9 scale as a practical screening tool for dehydration.

Main Methods:

• 15 healthy young men participated in three randomized 48-hour trials: euhydration, exercise-induced ID, and diuretic-induced ED.
• Dehydration levels were maintained at mild (1.9% for ID, 2.0% for ED).
• Diagnostic accuracy was assessed using receiver-operating characteristic-area under the curve (ROC-AUC).

Main Results:

• Several markers identified ID (e.g., urine color, plasma osmolality) and ED (e.g., postural heart rate change).
• Thirst 0-9 scale and urine osmolality identified both ID and ED with high accuracy (ROC-AUC > 0.78).
• The thirst 0-9 scale demonstrated a common threshold (≥4) with 100% sensitivity for ID and 87% for ED.

Conclusions:

• The thirst 0-9 scale is a valid and practical tool for screening mild intracellular and extracellular dehydration in young adults.
• A common dehydration threshold of ≥4 on the thirst 0-9 scale effectively identifies both types of mild dehydration.
• This finding supports the use of the thirst scale in clinical and athletic settings for dehydration assessment.