A patient with metabolic alkalosis has spot urine chloride of 8 mEq/L. Which cause fits this finding?
- A Primary hyperaldosteronism
- B Vomiting with gastric fluid loss ✓
- C Bartter syndrome
- D Diuretic abuse with active diuresis
Correct answer: B. Vomiting with gastric fluid loss
Explanation
A urine chloride below 10 to 20 mEq/L identifies chloride-depleted (saline responsive) alkalosis, typical of vomiting or prior diuretic use. In vomiting, gastric HCl loss depletes chloride and volume contraction stimulates avid proximal chloride reabsorption, so urine chloride stays very low. Hyperaldosteronism and Bartter syndrome are saline resistant with urine chloride above 20 mEq/L. Active loop or thiazide diuretic therapy itself forces chloriuresis, giving a high urine chloride during use.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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