skip to main content

High Anion Gap Metabolic Acidosis — RACP Adult Medicine MCQ

Instant feedback + full explanation. One question, done properly.

EasyNephrologyHigh Anion Gap Metabolic AcidosisRACP Adult Medicine

A 50-year-old man presents with altered mental status after a seizure. ABG shows pH 7.22, PaCO₂ 30 mmHg, HCO₃ 12 mmol/L, Na 140, K 4.5, Cl 100. What is the anion gap and what does it suggest?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — AG 28 – high anion gap metabolic acidosis

Anion gap = Na – (Cl + HCO₃) = 140 – (100 + 12) = 28 (normal 8–12). A high anion gap metabolic acidosis with respiratory compensation (low PaCO₂) is present. The common causes are remembered by the mnemonic GOLDMARK: Glycols (ethylene, propylene), Oxoproline (paracetamol metabolite), L-lactate, D-lactate, Methanol, Aspirin (salicylates), Renal failure (uraemia), Ketoacidosis (diabetic, alcoholic, starvation). Post-ictal lactic acidosis is a common cause but should be transient.

Reference: eTG – 2025 – Nephrology; AMH – 2025 – Acid-Base Disorders