A 25-year-old man presents with hypokalaemia (K⁺ 2.6 mmol/L), metabolic alkalosis (HCO3⁻ 32 mmol/L), normal blood pressure, and urinary chloride of 45 mmol/L. Serum magnesium is 0.52 mmol/L (low). Which diagnosis best explains this constellation?

• A Gitelman syndrome ✓
• B Bartter syndrome type I
• C Primary hyperaldosteronism
• D Diuretic abuse (thiazide)

Explanation

Gitelman syndrome is caused by loss-of-function mutations in the SLC12A3 gene encoding the thiazide-sensitive sodium-chloride cotransporter (NCC) in the distal convoluted tubule. It presents with hypokalaemia, metabolic alkalosis, normal to low blood pressure, and — crucially — hypomagnesaemia with hypocalciuria. The elevated urinary chloride (> 20 mmol/L) excludes vomiting (low urine Cl⁻). Bartter syndrome also presents similarly but classically with normocalciuria or hypercalciuria and usually in childhood with polyuria. Primary hyperaldosteronism causes hypertension. Thiazide abuse mimics Gitelman but should normalise after drug cessation; magnesium wasting is a hallmark feature of Gitelman.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.