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Enteric Hyperoxaluria — RACP Adult Medicine MCQ

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HardNephrologyEnteric HyperoxaluriaRACP Adult Medicine

A 45-year-old man presents with recurrent calcium oxalate kidney stones. His 24-hour urine shows elevated oxalate excretion (hyperoxaluria) with normal calcium. He has a history of Roux-en-Y gastric bypass surgery 3 years ago. What is the mechanism of his hyperoxaluria?

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Correct answer: A — Increased endogenous oxalate production

Following bariatric surgery (especially Roux-en-Y), fat malabsorption leads to enteric hyperoxaluria. Normally, dietary calcium binds oxalate in the gut, preventing its absorption. With fat malabsorption, calcium preferentially binds fatty acids (forming calcium soaps), leaving oxalate free for absorption (increased colonic oxalate permeability from bile salts further contributes). Management includes adequate hydration, calcium supplementation WITH meals (to bind oxalate), low-fat diet, and potassium citrate.

Reference: eTG – 2025 – Nephrology; EAU – 2024 – Urolithiasis Guidelines