Question:medium
A patient has Proteus infection and now plain xray of abdomen was done and a large stone was shown in urinary bladder. Stone is made up of
A patient has Proteus infection and now plain xray of abdomen was done and a large stone was shown in urinary bladder. Stone is made up of
Show Hint
Proteus = urease = alkaline urine = phosphate (infection) stone. Pick the phosphate option.
Updated On: Jun 22, 2026
- Calcium Phosphate
- Cysteine
- Calcium Oxalate
- Xanthine
Show Solution
The Correct Option is A
Solution and Explanation
Start from the bug, not the stone.
The examiner gives you one decisive word: Proteus. Proteus mirabilis is the prototype UREASE-positive uropathogen, and urease is the enzyme that links infection to a specific stone chemistry. So the question is really "which stone does an alkaline, urease-driven urine make?"
Trace the chemistry.
Urease hydrolyses urea to ammonia and carbon dioxide:
\[\text{Urea} \xrightarrow{\text{urease}} 2\,\text{NH}_3 + \text{CO}_2\]
The liberated ammonia drives urinary pH up. Alkaline urine is supersaturated for magnesium ammonium phosphate (struvite) and for carbonate-apatite (calcium phosphate), so these phosphate salts crystallise out and can build into a large, often staghorn or bladder, infection stone that is radio-opaque on plain film - matching the X-ray finding.
Map to the options.
Only one listed salt is a phosphate that precipitates in this alkaline, infection setting: calcium phosphate. The other three each belong to a different, non-infective mechanism:
$\bullet$ Cystine - inherited cystinuria, acidic urine, hexagonal crystals.
$\bullet$ Calcium oxalate - the commonest stone, but driven by metabolic/dietary factors in acidic urine, not by urease.
$\bullet$ Xanthine - rare enzyme defect/drug-related, radiolucent.
These struvite/phosphate stones precipitate fast in the supersaturated alkaline urine, are radio-opaque, and characteristically enlarge into bulky staghorn or bladder calculi exactly as described in the stem. Therefore the Proteus (urease) stone here is calcium phosphate (A).
The examiner gives you one decisive word: Proteus. Proteus mirabilis is the prototype UREASE-positive uropathogen, and urease is the enzyme that links infection to a specific stone chemistry. So the question is really "which stone does an alkaline, urease-driven urine make?"
Trace the chemistry.
Urease hydrolyses urea to ammonia and carbon dioxide:
\[\text{Urea} \xrightarrow{\text{urease}} 2\,\text{NH}_3 + \text{CO}_2\]
The liberated ammonia drives urinary pH up. Alkaline urine is supersaturated for magnesium ammonium phosphate (struvite) and for carbonate-apatite (calcium phosphate), so these phosphate salts crystallise out and can build into a large, often staghorn or bladder, infection stone that is radio-opaque on plain film - matching the X-ray finding.
Map to the options.
Only one listed salt is a phosphate that precipitates in this alkaline, infection setting: calcium phosphate. The other three each belong to a different, non-infective mechanism:
$\bullet$ Cystine - inherited cystinuria, acidic urine, hexagonal crystals.
$\bullet$ Calcium oxalate - the commonest stone, but driven by metabolic/dietary factors in acidic urine, not by urease.
$\bullet$ Xanthine - rare enzyme defect/drug-related, radiolucent.
These struvite/phosphate stones precipitate fast in the supersaturated alkaline urine, are radio-opaque, and characteristically enlarge into bulky staghorn or bladder calculi exactly as described in the stem. Therefore the Proteus (urease) stone here is calcium phosphate (A).
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