Dehydration
A shortage of body water, from taking in too little or losing too much through vomiting, diarrhoea, sweating or fever. Usually mild and easily corrected by drinking, but severe dehydration strains the kidneys and circulation and can be dangerous, especially in the very young and old.
What it is
Dehydration is a state where the body has lost more fluid than it has taken in, so there is not enough water for it to work normally. It develops when intake is too low or losses are high — through vomiting and diarrhoea, heavy sweating, fever, poorly controlled diabetes (passing large amounts of urine), diuretic medicines, or simply not drinking enough, especially in hot weather. Mild dehydration causes thirst, a dry mouth, dark and reduced urine, tiredness and light-headedness. As it worsens, blood pressure falls, the heart races, the kidneys receive less blood and their waste markers rise, and confusion or collapse can follow. It is especially risky at the extremes of age — babies and young children lose fluid quickly with illness, and older people may feel less thirst and be on medicines that increase losses. On blood tests, the kidney markers rise together (urea typically more than creatinine), and sodium and the haematocrit often rise as the blood concentrates.
Key lab markers
- Urea — rises, often more than creatinine (a high urea-to-creatinine ratio is a classic clue).
- Creatinine and eGFR — kidney function can dip when severely dehydrated (pre-renal).
- Sodium — often high-normal or raised as the blood concentrates.
- Haematocrit — rises as plasma volume falls.
- Urine — concentrated (dark, high specific gravity).
- Glucose — checked, as uncontrolled diabetes is an important cause.
Symptoms
- Thirst and a dry mouth
- Dark, strong-smelling urine, passing less than usual
- Tiredness, light-headedness or dizziness, especially on standing
- Headache
- A fast heartbeat
- Dry skin and lips, sunken eyes
- In babies: a sunken soft spot, fewer wet nappies, no tears when crying, drowsiness
- Severe: confusion, very low blood pressure, collapse
Related symptoms
Related lab panels
When to discuss with a doctor
Mild dehydration is corrected by drinking fluids, ideally with some salt and sugar (oral rehydration) if losses are from vomiting or diarrhoea. Seek medical help if someone cannot keep fluids down, has severe or ongoing diarrhoea and vomiting, passes very little or no urine, is confused, dizzy on standing, or has a fast heartbeat, and urgently for a baby or young child with signs of dehydration, an older person who is unwell, or anyone with drowsiness or collapse — severe dehydration may need fluids into a vein. Uncontrolled diabetes causing heavy urination and thirst needs prompt attention. Mediora.AI can flag the raised urea, sodium and haematocrit pattern that fits dehydration and separate it from a primary kidney problem; the clinical assessment belongs with your doctor.