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Lithium toxicity — SCE Acute Medicine MCQ

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ModerateToxicology and OverdoseLithium toxicitySCE Acute Medicine

A 70-year-old woman is assessed on the acute medical unit. She takes lithium and develops tremor, ataxia and diarrhoea after starting an ACE inhibitor. Creatinine is above baseline. Initial assessment includes relevant observations, bedside tests and urgent blood results. What is the most appropriate investigation?

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Correct answer: E — Serum lithium concentration with renal function

Serum lithium concentration with renal function is the best answer because lithium toxicity is precipitated by renal impairment and interacting drugs, so lithium level and renal function guide treatment. Coagulation profile including fibrinogen and D-dimer is plausible, but it is less appropriate for the physiology or timing described in this stem. The other distractors either fit a neighbouring presentation, delay definitive treatment, or miss the key immediate risk. Clinical pearl: Symptoms may correlate poorly with a single level in chronic toxicity.

Reference: https://bnf.nice.org.uk/#acute-medicine-order-48-1