Potassium (Urine)

Urine Electrolytes are measured to assess kidney function, fluid balance and the body's electrolyte status.

Urinary electrolyte levels, particularly sodium and potassium, indicate how well the kidneys are managing electrolyte and fluid balance.

Urinary sodium concentration is used to distinguish between pre-renal and intrinsic causes of acute kidney injury (AKI):

• A low urinary sodium level (<20 mEq/L) indicates pre-renal causes (dehydration, hypovolaemia).
• A high urinary sodium level (>40 mEq/L) indicates intrinsic renal damage (e.g. acute tubular necrosis).
• Hyponatremia/hypernatremia: A low urinary sodium level in the setting of hyponatremia indicates a non-renal cause (e.g. heart failure, cirrhosis of the liver).
• High urinary sodium in hyponatremia suggests renal salt loss or inappropriate secretion of antidiuretic hormone (SIADH).
• Hypokalaemia/hyperkalaemia: Urinary potassium excretion helps determine whether potassium imbalances are due to renal or non-renal causes.
• A high level of urinary potassium in hypokalaemia suggests renal potassium loss (e.g. diuretics, hyperaldosteronism). A low urinary potassium level suggests extrarenal losses (e.g. gastrointestinal losses such as diarrhoea).
• Chloride in metabolic alkalosis: Urinary chloride levels are used to distinguish the causes of metabolic alkalosis. A low urinary chloride level (<20 mEq/L) suggests a chloride-responsive cause (e.g. vomiting or diuretic use), whereas a high urinary chloride level indicates non-chloride-responsive conditions (e.g. primary hyperaldosteronism).