A 55-year-old hypertensive man has pH 7.50, HCO3- 34 mEq/L, K+ 2.9 mEq/L. Spot urine chloride is 45 mEq/L. Which category does his metabolic alkalosis belong to?
- A Chloride responsive, due to volume depletion
- B Chloride resistant, suggesting mineralocorticoid excess ✓
- C Chloride responsive, due to diuretic use within 24 hours
- D Saline unresponsive, due to severe potassium deficiency alone
Correct answer: B. Chloride resistant, suggesting mineralocorticoid excess
Explanation
A urine chloride above 20 mEq/L marks chloride-resistant metabolic alkalosis, and with hypertension plus hypokalaemia the classic cause is primary aldosteronism, where aldosterone-driven H+ and K+ secretion persists regardless of volume. Chloride-responsive alkalosis from vomiting or diuretics shows urine chloride below 20 mEq/L and corrects with saline. Note that active diuretic use can transiently raise urine chloride, so the drug history must be excluded before labelling a case resistant.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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