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Cirrhotic Dilutional Hyponatraemia — RACP Adult Medicine MCQ

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ModerateGastroenterologyCirrhotic Dilutional HyponatraemiaRACP Adult Medicine

A 60-year-old man with decompensated cirrhosis (Child-Pugh C) has Na⁺ 125 mmol/L. He has tense ascites, peripheral oedema, and raised JVP. Serum osmolality 265 mOsm/kg. Urine Na⁺ is 5 mmol/L. Urine osmolality 450 mOsm/kg. What is the most likely cause?

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Correct answer: D — Cirrhosis

Hypervolaemic hyponatraemia (oedematous — ascites, oedema) with very low urine Na⁺ (<10 mmol/L) in decompensated cirrhosis is dilutional hyponatraemia from non-osmotic ADH release (reduced effective arterial blood volume activates RAAS and ADH). Urine Na⁺ <10 distinguishes from SIADH (urine Na⁺ >30). Treatment: fluid restriction, avoid rapid correction (cirrhotic brain is vulnerable to ODS). Tolvaptan may be considered cautiously.

Reference: European Hyponatraemia Guidelines 2023; GESA 2024