Acute & emergency · UKMLA & AKT
Dehydration
A free high-yield preview for the UKMLA Applied Knowledge Test. Below are the key points to recognise dehydration — the full SA Note notes add investigations, management, complications and 10 practice questions.
Key high-yield points
- 🥇 First-line
- U&E - raised urea/creatinine (pre-renal AKI), sodium level (hypernatraemia = hypotonic loss; hyponatraemia = isotonic/hypotonic loss), potassium (GI losses cause hypokalaemia)
- FBC - raised haematocrit/haemoglobin from haemoconcentration
- Urinalysis - concentrated urine (specific gravity >1.020) supports dehydration
- Blood glucose - exclude hyperglycaemia/osmotic diuresis
- Venous blood gas - pH (metabolic acidosis), lactate (poor tissue perfusion), bicarbonate
- 🏆 Gold standard
- Plasma osmolality - 90% sensitivity, 100% specificity; >295 mOsm/kg confirms hyperosmolar dehydration. Calculated as: 2[Na+] + glucose + urea (mmol/L)
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