Urology: struvite calculi: 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: struvite calculi

Sample item

A 45-year-old woman with recurrent urinary infections has a staghorn calculus on imaging, and her urine pH is 8.0. Which stone and organism are most likely?

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

The answer and the reasoning

D. Magnesium ammonium phosphate stone with Proteus mirabilis

Urease-producing bacteria such as Proteus, Klebsiella and Providencia split urea to ammonia, raising urine pH and precipitating magnesium ammonium phosphate (struvite) and carbonate apatite. These stones grow rapidly into staghorn shapes and are radio-opaque. Treatment is percutaneous nephrolithotomy with complete clearance, as residual fragments perpetuate infection.

Option by option

  • A. Calcium oxalate stone with Escherichia coli

    Calcium oxalate stones form in acidic to neutral urine and are not linked to alkaline infection.

  • B. Uric acid stone with Klebsiella

    Uric acid stones form in acidic urine.

  • C. Cystine stone with Pseudomonas aeruginosa

    Cystine stones are due to cystinuria, form in acidic urine and are not infection stones.

  • D. Magnesium ammonium phosphate stone with Proteus mirabilis (correct)

    Urease-producing Proteus alkalinises urine and forms infection (struvite) stones.

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.

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Questions about this General Surgery question

What is the answer to this General Surgery question?

The best answer is D, Magnesium ammonium phosphate stone with Proteus mirabilis. Urease-producing bacteria such as Proteus, Klebsiella and Providencia split urea to ammonia, raising urine pH and precipitating magnesium ammonium phosphate (struvite) and carbonate apatite.

Why is "Calcium oxalate stone with Escherichia coli" not the answer?

Calcium oxalate stones form in acidic to neutral urine and are not linked to alkaline infection.

Why is "Uric acid stone with Klebsiella" not the answer?

Uric acid stones form in acidic urine.

Why is "Cystine stone with Pseudomonas aeruginosa" not the answer?

Cystine stones are due to cystinuria, form in acidic urine and are not infection stones.

What concept does this question test?

It tests Urology: struvite calculi in General Surgery. These stones grow rapidly into staghorn shapes and are radio-opaque. Treatment is percutaneous nephrolithotomy with complete clearance, as residual fragments perpetuate infection.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: struvite calculi?

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.