BRCU Online 2026: Test Your Knowledge
A 45-year-old woman presents to the emergency department with syncope. Her BP is 100/80 mm Hg, and physical exam is within normal limits.
Her initial laboratory values are as follows:
- pH 7.48
- PCO2 45 mm Hg
- Na 140 mEq/L
- Cl 100 mEq/L
- K 2.1 mEq/L
- HCO3 32 mEq/L
- BUN 18 mg/dL
- Cr 1.0 mg/dL
- Glucose 100 mg/dL
- Urine free cortisol: cortisone (24-hour): 0.5
- Urine Cl: 50 mEq/L
Which of the following is the most likely explanation for these laboratory values?
- Laxative use
- Gitelman syndrome
- Apparent mineralocorticoid excess
- Liddle syndrome
- Renal artery stenosis
Show Answer
Reference:
Parmar MS, Muppidi V, Bashir K. "Gitelman Syndrome." In:
StatPearls. StatPearls Publishing; last updated April 7, 2024. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459304/
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Explanation
The initial approach to a patient with metabolic alkalosis and hypokalemia is to first assess volume status and BP, and then stratify by urinary Cl level if there is evidence of hypovolemia: a low urine Cl value suggests a differential diagnosis of extrarenal Cl depletion, such as vomiting, chloride-rich diarrhea, or cystic fibrosis. If the urine Cl level is high, the differential diagnosis includes diuretic use, Bartter syndrome, and Gitelman syndrome. Although laxative abuse most commonly presents with hypokalemia and a normal anion gap acidosis, if the stool content is rich in Cl, it can give rise to a metabolic alkalosis. However, the elevated urine Cl level in this case excludes laxative abuse as a cause. Of the remaining answer choices, all would have an elevated urinary Cl level, but only Gitelman syndrome could cause of this patient's presentation with syncope and low BP. The remaining choices would present with resistant hypertension.
