Forty-eight hours after induction chemotherapy for acute lymphoblastic leukaemia, a 12-year-old boy develops serum potassium 6.4 mEq/L, phosphate 8.2 mg/dL, uric acid 14 mg/dL, calcium 6.8 mg/dL, and creatinine rising from 0.7 to 2.4 mg/dL. Which set of changes defines this syndrome?

• A Hypernatraemia, hyperphosphataemia, hyperuricaemia, and hypocalcaemia
• B Hyperkalaemia, hypophosphataemia, hyperuricaemia, and hypercalcaemia
• C Hypokalaemia, hyperphosphataemia, hypouricaemia, and hypocalcaemia
• D Hyperkalaemia, hyperphosphataemia, hyperuricaemia, and hypocalcaemia ✓

Explanation

Tumour lysis syndrome follows rapid lysis of a large tumour cell burden after chemotherapy. Release of intracellular contents produces hyperkalaemia, hyperphosphataemia, and hyperuricaemia, while calcium falls because phosphate binds calcium as calcium phosphate, precipitating in tissues. The combination of all four electrolyte derangements plus AKI is diagnostic by the Cairo-Bishop definition. Hypophosphataemia and hypercalcaemia are physiologically impossible here because phosphate release always accompanies cell lysis.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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