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The four main kidney stone types — what they're made of, who gets them, and how each is prevented. Stone composition drives treatment, so knowing the type matters.
Evidence reviewed & updated: 2026-08 — reflects the latest published trials and guidelines.
About 80% of kidney stones are calcium-based (mostly calcium oxalate), 5-10% are uric acid, 5-10% struvite (infection stones), and 1-2% cystine. Each type has different causes and different prevention strategies — which is why stone analysis and a 24-hour urine test are the foundation of prevention.
Calcium oxalate stones form when urine is supersaturated with calcium and oxalate — low urine volume concentrates both. Key drivers: not drinking enough water, high sodium intake (sodium increases calcium excretion), high-oxalate foods in some people, and low dietary calcium (contrary to intuition, low calcium intake RAISES oxalate absorption).
Calcium phosphate stones are less common and form in alkaline urine (high pH). They're associated with renal tubular acidosis, hyperparathyroidism, and some medications. Both calcium types respond to the same foundation: 2-2.5 L urine per day, salt restriction, and normal dietary calcium.
Uric acid stones form in persistently acidic urine (low pH) — common in gout, metabolic syndrome, diabetes, and after weight-loss surgery. Unlike calcium stones, they can often be DISSOLVED by alkalinizing the urine (potassium citrate) — and prevention targets raising urine pH above 6.0 plus reducing uric acid load (allopurinol where needed).
They're radiolucent (don't show on plain X-ray) — often found on ultrasound or CT.
Struvite stones grow from urease-producing bacteria (Proteus, Klebsiella, Pseudomonas) that alkalinize urine and produce ammonium-magnesium-phosphate crystals. They can grow large ('staghorn' stones filling the kidney) and are more common in women and people with recurrent UTIs or urinary diversions.
Treatment is aggressive: complete stone removal (surgery) plus antibiotics, because residual fragments perpetuate infection. Prevention = urinary tract infection control.
Cystinuria is a genetic disorder causing excessive cystine excretion — stones start in childhood and recur throughout life. Cystine stones need aggressive hydration (very high fluid targets), urine alkalinization, and often cystine-binding medications (tiopronin, penicillamine).
Early diagnosis matters: a child or young adult with recurrent stones should be tested for cystinuria (urine cystine).
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