A 30-year-old woman presents with muscle weakness and a serum potassium of 2.8 mEq/L. Her urine K+ is 45 mEq/day (elevated). ABG shows metabolic alkalosis. Which mechanism most likely explains her hypokalemia?

• A Diarrhea with extrarenal K+ loss
• B Transcellular shift of K+ into cells from alkalosis alone
• C Decreased dietary potassium intake
• D Renal K+ wasting due to excess aldosterone effect ✓

Explanation

Urinary K+ excretion >20-25 mEq/day in the setting of hypokalemia indicates renal potassium wasting. Combined with metabolic alkalosis, the most likely cause is primary or secondary hyperaldosteronism, which drives principal cell Na+ reabsorption and K+ secretion. Diarrhea causes extrarenal loss with low urine K+ (<15 mEq/day). Metabolic alkalosis alone causes only a mild shift of K+ into cells, not persistent urinary K+ wasting of this magnitude.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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