Types of Kidney Stones

Kidney stones are broadly classified by their mineral composition. In Australia and the UK, the approximate distribution is:^{1, 2}

Calcium stones - roughly 80% (calcium oxalate more common than calcium phosphate).
Uric acid stones - roughly 5-10%.
Struvite (infection) stones - roughly 5-10%, more common in women.
Cystine stones - rare (under 1%), usually hereditary.
Rarer types - drug-related stones, matrix stones, xanthine stones.

Calcium stones

The most common stone type. Calcium oxalate and calcium phosphate. Best prevented with adequate fluid, normal dietary calcium, and reduced sodium.

Uric acid stones

Associated with gout, obesity, and persistently acidic urine. The only stone type that can often be dissolved with medication.

Struvite stones

Caused by urea-splitting bacteria. Can grow rapidly into stag-horn stones. Definitive surgery is essential.

Cystine stones

Inherited defect in cystine reabsorption. Recurrent stones from childhood. Lifelong medical management required.

Why the type matters

Stone composition influences three practical decisions:

How the stone is treated. Very hard stones (pure calcium oxalate monohydrate, cystine) respond less well to shockwave lithotripsy and are usually better treated with ureteroscopy or PCNL. Uric acid stones are often the easiest to dissolve with tablets alone.
How recurrence is prevented. Calcium stones are best prevented with hydration and diet; uric acid stones with urinary alkalinisation (potassium citrate); struvite stones by eradicating infection; cystine stones with lifelong alkalinisation and thiol-binding medication.
What follow-up is needed. Patients with rare stone types are usually managed with a renal physician colleague in a dedicated metabolic clinic.

How the stone type is identified

Wherever possible, a stone that is passed or retrieved should be sent for infrared spectroscopy or x-ray diffraction. The result is typically reported within a week and guides prevention.³

When no stone is available, the composition can often be inferred from:

The stone's density on CT (Hounsfield units).
Urine pH (persistently acidic in uric acid stones, persistently alkaline in struvite).
24-hour urine biochemistry.
Clinical context (a febrile stone former with an elevated urine pH strongly suggests struvite).

References

Sewell J, et al. Urolithiasis - ten things every general practitioner should know. Australian Family Physician. 2017.
Leslie SW, Sajjad H, Murphy PB. Nephrolithiasis. StatPearls. 2024.
Skolarikos A, et al. EAU Guidelines on Urolithiasis. 2025.