Struvite (infection) kidney stones

Why struvite stones form

Certain bacteria - most commonly Proteus, Klebsiella, Pseudomonas, and Staphylococcus species - produce an enzyme called urease. Urease splits urea in the urine into ammonia and carbon dioxide, driving the urine strongly alkaline (pH often above 7.2) and super-saturating it with magnesium ammonium phosphate crystals - the chemical name for struvite.¹

Struvite stones therefore do not form without persistent urinary infection with a urease-producing organism. They are most common in:

• Women with recurrent urinary tract infections.
• Patients with long-term urinary catheters or neurogenic bladders.
• Patients with anatomical abnormalities that impair bladder emptying or urinary drainage.
• Patients with a previous urinary reconstruction using bowel.

How struvite stones present

Struvite stones often grow silently, detected only when the patient presents with:

• Recurrent urinary infections, often with the same organism.
• Dull flank pain or a feeling of heaviness, rather than classic renal colic.
• Haematuria.
• Sepsis if drainage becomes obstructed.
• A stag-horn stone found on imaging done for another reason.

Imaging and diagnosis

CT KUB confirms the size and shape of the stone and defines the branching anatomy of stag-horn stones. A urine culture identifies the offending organism. Because struvite stones form in alkaline urine, a persistently high urine pH in a stone former - particularly a woman with recurrent infections - is a strong clue.

Why struvite stones must be completely cleared

Any fragment of a struvite stone left behind after surgery acts as a reservoir of infection. Antibiotics cannot penetrate into the stone material, and the residual fragment becomes a focus for re-infection and regrowth. International guidelines are clear: the aim of struvite stone surgery is complete stone clearance, not just debulking.¹

Treatment

Most struvite and stag-horn stones are large and branched, which makes them poor candidates for shockwave lithotripsy.

• Percutaneous nephrolithotomy (PCNL) is the first-line surgical treatment for stag-horn stones and is recommended in both the EAU 2025 and AUA 2026 guidelines.^{1, 2}
• Staged or combined procedures - often PCNL with flexible ureteroscopy at the same sitting, or a second-look PCNL - are sometimes needed to clear every fragment.
• Targeted antibiotics guided by the urine culture are given around the operation; a longer course is sometimes required after surgery.
• Addressing the underlying cause - treating incomplete bladder emptying, removing or changing catheters, correcting anatomical problems - is essential to prevent recurrence.

Prevention and follow-up

• Regular surveillance imaging (usually low-dose CT KUB or plain x-ray) for at least several years after treatment, because struvite stones can recur silently.
• Culture-guided antibiotic treatment of any urinary infection.
• Prevention of bladder stasis - optimising bladder emptying, considering intermittent self-catheterisation rather than long-term indwelling catheters where feasible.
• Methenamine hippurate may be considered in selected patients to reduce bacterial growth.

Related pages

References

1. Skolarikos A, et al. EAU Guidelines on Urolithiasis. 2025.
2. Pearle MS, et al. Surgical Management of Kidney and Ureteral Stones: AUA Guideline (2026).