Калий (К) в моче\Potassium (urine)

The Potassium, 24‑Hour Urine test measures total potassium excreted over a day to assess potassium homeostasis and the broader water–electrolyte balance. It is used to differentiate renal from extrarenal potassium losses, to evaluate kidney and adrenal (aldosterone) function, and to monitor the impact of potassium supplementation or medications that influence electrolyte transport. This assay is also referred to as urine potassium or 24‑hour urinary potassium.

Potassium is the principal intracellular cation and tightly interrelated with sodium and other ions. The distribution of sodium extracellularly and potassium intracellularly maintains osmotic balance, circulating volume, transmembrane transport, and neuromuscular conduction. Intestinal and renal mechanisms regulate total‑body potassium. In the kidney, potassium is secreted in the distal tubules and collecting ducts in exchange for sodium, while substantial reabsorption occurs in the proximal tubules; proximal tubular injury can therefore deplete body potassium. Renal potassium loss depends on distal sodium delivery, the local hydrogen ion concentration, and aldosterone activity. In metabolic alkalosis, urinary potassium excretion increases and serum potassium commonly falls. Excessive renal potassium loss can result from enhanced distal sodium–potassium exchange driven by mineralocorticoids or glucocorticoids, inhibition of the sodium pump, impaired tubular reabsorption, or Fanconi syndrome associated with hypercalcemia. Patterns of serum and urine potassium help localize the cause of dyskalemia: hypokalemia may coexist with hyperkaluria, whereas hyperkalemia is often accompanied by hypokaluria. Quantifying 24‑hour potassium excretion supports this distinction: values greater than 30 mmol/day (or > 15 mmol/L) suggest renal or adrenal causes, while extrarenal losses—such as diarrhea, villous adenoma, or laxative overuse—typically produce less than 25 mmol/day (or < 15 mmol/L). Interpretation should integrate the clinical presentation alongside serum potassium and other key electrolytes.