Thiazide-Induced Hyponatraemia — RACP Adult Medicine MCQ

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ModerateNephrologyThiazide-Induced HyponatraemiaRACP Adult Medicine

A 70-year-old woman started on hydrochlorothiazide 2 weeks ago for hypertension presents with Na⁺ 122 mmol/L. She is mildly volume depleted. Urine Na⁺ is 35 mmol/L. K⁺ is 3.0 mmol/L. What is the most likely cause?

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Correct answer: C — Thiazide-induced hyponatraemia

Hyponatraemia with hypokalaemia shortly after thiazide initiation in an elderly woman is thiazide-induced hyponatraemia. Thiazides impair diluting capacity (block NaCl reabsorption in the distal convoluted tubule) and stimulate ADH release. Risk factors: elderly women, low body mass, low dietary solute intake. Can be severe and occur within 1-2 weeks. Management: cease thiazide, correct Na⁺ slowly, replace K⁺.

Reference: AMH – 2025 – Thiazide Hyponatraemia; European Hyponatraemia Guidelines 2023