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Ammonia in HE — RACP Adult Medicine MCQ

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EasyGeneral Internal MedicineAmmonia in HERACP Adult Medicine

A 55-year-old man with alcoholic cirrhosis develops encephalopathy and elevated ammonia. He has not had a prior episode. Which is the correct statement about ammonia measurement?

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Correct answer: A — Ammonia levels correlate poorly with HE severity – diagnosis is clinical

Hepatic encephalopathy is a CLINICAL diagnosis. While ammonia is often elevated in HE, levels correlate poorly with HE grade, and a normal ammonia does NOT exclude HE. Serial ammonia measurements should NOT be used to guide lactulose dosing or treatment escalation. Factors affecting ammonia measurement include sample handling (must be on ice, processed within 30 minutes), tourniquet application, exercise, and diet. Arterial ammonia is more accurate than venous. The West Haven criteria grade HE clinically (Grade I: sleep disturbance, impaired concentration → Grade IV: coma). Lactulose dosing is titrated to stool output (2–3 soft stools/day), NOT ammonia levels.

Reference: eTG – 2025 – Gastrointestinal; EASL – 2022 – Hepatic Encephalopathy Guidelines