skip to main content

Proteus Struvite Stones — SCE Infectious Diseases MCQ

Instant feedback + full explanation. One question, done properly.

EasyHealthcare-Associated InfectionsProteus Struvite StonesSCE Infectious Diseases

A 50-year-old man with a copper IUD in his urinary bladder (misplaced during attempted IUD insertion) develops recurrent Proteus mirabilis UTIs with bladder stone formation. What is the relationship between Proteus and stone composition?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: B — Proteus produces urease which raises urinary pH, causing struvite (magnesium ammonium phosphate) stone formation — the foreign body (IUD) acts as a nidus

Proteus mirabilis (and other urease-producing organisms: Klebsiella, Providencia, Morganella, some Staphylococci) converts urea to ammonia via urease, alkalinising urine to pH >7. This promotes crystallisation of magnesium ammonium phosphate (struvite) and calcium phosphate (apatite), forming 'infection stones' or 'staghorn calculi.' The foreign body (misplaced IUD) provides a nidus for both bacterial biofilm and stone formation. Management requires: stone removal, foreign body removal, and targeted antibiotics. Without removing the source, recurrence is inevitable.

Reference: EAU 2024 – Urolithiasis; NICE NG109 2018 – UTI