Urology: enteric hyperoxaluria: practice question

A General Surgery question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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General Surgery · Urology: enteric hyperoxaluria

Sample item

A man who had an extensive ileal resection for Crohn disease develops recurrent calcium oxalate stones. What is the underlying mechanism?

APrimary hyperparathyroidism causes hypercalcaemia and hypercalciuriaBUrease-producing bacteria raise urinary pH and precipitate oxalateCFat malabsorption binds calcium in the gut, so more free oxalate is absorbed from the colonDExcess intake of vitamin C raises the endogenous oxalate pool

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Fat malabsorption binds calcium in the gut, so more free oxalate is absorbed from the colon

In fat malabsorption, unabsorbed fatty acids bind calcium so less calcium is available to bind oxalate in the lumen. Free oxalate is absorbed in the colon and excreted in urine, producing stones. Treatment includes a low-fat, low-oxalate diet, calcium with meals and fluids.

Option by option

A. Primary hyperparathyroidism causes hypercalcaemia and hypercalciuria
Hyperparathyroidism causes calcium stones through hypercalciuria and is not related to ileal resection.
B. Urease-producing bacteria raise urinary pH and precipitate oxalate
Urease-producing bacteria cause struvite stones, not calcium oxalate stones.
C. Fat malabsorption binds calcium in the gut, so more free oxalate is absorbed from the colon (correct)
Correct. Calcium is trapped by fatty acids, leaving oxalate free for colonic absorption.
D. Excess intake of vitamin C raises the endogenous oxalate pool
Vitamin C excess can raise oxalate but is not the mechanism after ileal resection.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this General Surgery question

What is the answer to this General Surgery question?

The best answer is C, Fat malabsorption binds calcium in the gut, so more free oxalate is absorbed from the colon. In fat malabsorption, unabsorbed fatty acids bind calcium so less calcium is available to bind oxalate in the lumen.

Why is "Primary hyperparathyroidism causes hypercalcaemia and hypercalciuria" not the answer?

Hyperparathyroidism causes calcium stones through hypercalciuria and is not related to ileal resection.

Why is "Urease-producing bacteria raise urinary pH and precipitate oxalate" not the answer?

Urease-producing bacteria cause struvite stones, not calcium oxalate stones.

Why is "Excess intake of vitamin C raises the endogenous oxalate pool" not the answer?

Vitamin C excess can raise oxalate but is not the mechanism after ileal resection.

What concept does this question test?

It tests Urology: enteric hyperoxaluria in General Surgery. Free oxalate is absorbed in the colon and excreted in urine, producing stones. Treatment includes a low-fat, low-oxalate diet, calcium with meals and fluids.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Urology: enteric hyperoxaluria?

Learn classic signs and eponyms alongside what they diagnose. Then use the flashcards and the other General Surgery questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.