An 8-year-old boy with newly diagnosed high-burden acute lymphoblastic leukemia begins induction chemotherapy. Forty-eight hours later he develops oliguria, and labs show potassium of 6.8 mEq/L, phosphate of 9 mg/dL, calcium of 6.5 mg/dL and uric acid of 15 mg/dL. Which complication poses the most immediate threat to life?
- A Hyperuricemia causing acute urate nephropathy
- B Hyperphosphatemia causing metastatic calcification of the cornea
- C Hyperkalemia precipitating fatal cardiac arrhythmia ✓
- D Hypocalcemia causing tetany and laryngospasm
Correct answer: C. Hyperkalemia precipitating fatal cardiac arrhythmia
Explanation
Lysis of the massive leukaemic cell load releases intracellular potassium, phosphate and purines. Potassium rises fastest and can trigger ventricular arrhythmia within hours, making it the first life-threatening emergency to address with cardioprotective measures and shift strategies. Uric acid crystallisation (option A) causes renal failure over days, and hypocalcemia (option D) results from phosphate binding calcium, developing more gradually than hyperkalemic cardiotoxicity.
Reference: Nelson Textbook of Pediatrics, 22nd ed.
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