Struvite (staghorn) calculus
Struvite (magnesium ammonium phosphate) stones form when urease-splitting organisms, most often Proteus mirabilis, raise urine pH above 7.5 and precipitate coffin-lid crystals that rapidly grow into staghorn calculi bridging multiple renal calyces. Diagnosis is by imaging plus alkaline urine and urease-positive culture, and treatment requires both antibiotic control of the infection and complete surgical stone removal, typically percutaneous nephrolithotomy, since incomplete clearance predisposes to recurrence, sepsis, and progressive kidney loss.
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What this article covers
- Overview
An infection stone, not a metabolic one: struvite (magnesium ammonium phosphate) calculi form only in the presence of urease-splitting bacteria, most commonly Proteus mirabilis, distinguishing them…
- Epidemiology
Struvite stones account for roughly 9% to 15% of all kidney stones, the second or third most common composition after calcium-containing stones.
- Risk factors
Chronic or recurrent urinary tract infection with a urease-splitting organism, above all Proteus mirabilis, the dominant driver of struvite formation.
- Pathophysiology
Urease-producing bacteria hydrolyze urea into ammonium and carbon dioxide: Proteus mirabilis is the most common organism, with Klebsiella, Pseudomonas, and some staphylococcal species (including…
- Clinical features
Symptoms and signs are those of the underlying chronic or recurrent urinary tract infection (dysuria, urinary frequency, cloudy or foul-smelling urine, low-grade fever, flank discomfort), rather than…
- Differential diagnosis
Calcium oxalate/calcium phosphate nephrolithiasis: distinguished by neutral to acidic (oxalate) or alkaline (phosphate) urine pH without an active urease-producing infection, and by a metabolic risk…
- Diagnosis
Struvite staghorn calculus is confirmed by imaging demonstrating a calculus filling and bridging two or more renal calyces, together with alkaline urine (pH above 7.5) and a urine culture growing a…
- Management
First, assess for acute infection and sepsis physiology.
- Complications
Urosepsis: from an infected, obstructing staghorn stone; the most immediately life-threatening complication, requiring emergent decompression and antibiotics.
- Prognosis
Untreated struvite staghorn calculi carry the worst prognosis among stone types, with progressive risk of sepsis, recurrent infection, and end-stage kidney disease.
- Prevention
Treat every urinary tract infection to completion, with a post-treatment test-of-cure urine culture in patients with prior struvite stones, to prevent seeding of a new infection stone.
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