Dehydration
Dehydration occurs when the body loses more fluid than it takes in, and does not have enough water to carry out its normal functions. Even mild dehydration can affect concentration, energy levels and physical performance.
Common causes include not drinking enough fluids, excessive sweating, diarrhoea, vomiting and fever. Older adults, young children and people with chronic conditions are at greater risk.
Blood tests for electrolytes such as sodium and chloride help assess hydration status and the body's fluid balance. Abnormal levels can indicate dehydration or underlying conditions affecting the kidneys or hormonal regulation.
Symptoms of dehydration include thirst, dark-coloured urine, dizziness, fatigue and dry mouth. Severe dehydration is a medical emergency and requires prompt treatment.
Causes of Dehydration
Dehydration occurs when fluid output exceeds fluid intake. Common causes include:
- Inadequate fluid intake, which is particularly common in older adults who may have a reduced sense of thirst
- Diarrhoea and vomiting, which can cause rapid fluid and electrolyte loss
- Excessive sweating from exercise, hot weather or fever
- Diabetes, where high blood glucose levels cause increased urination
- Diuretic medications, which increase urine production
- Alcohol, which has a diuretic effect
Electrolyte imbalances in sodium and chloride levels can result from dehydration or from conditions affecting the kidneys, adrenal glands or pituitary gland.
Tests that can help check this condition
Learn more on the official NHS page .
