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Post-Renal Obstructive AKI — RACP Adult Medicine MCQ

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EasyNephrologyPost-Renal Obstructive AKIRACP Adult Medicine

A 75-year-old man with BPH develops AKI. Creatinine 500 μmol/L. He has not passed urine for 18 hours. Bladder scan shows 1200 mL residual. USS shows bilateral hydronephrosis. After catheterisation, 1500 mL drains immediately and urine output becomes 300 mL/hr (post-obstructive diuresis). What is the AKI type?

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Correct answer: D — Post-renal (obstructive) AKI

Anuria + distended bladder + bilateral hydronephrosis + immediate diuresis after catheterisation = post-renal (obstructive) AKI from urinary retention (BPH). Post-obstructive diuresis (POD) can be profound (litres/day) and requires IV fluid replacement to prevent hypovolaemia and electrolyte disturbance. Monitor electrolytes closely. Creatinine typically normalises within days if obstruction is relieved early.

Reference: KDIGO – 2024 – AKI; eTG Nephrology 2024