October 2026 English edition · Evidence reviewed through October 3, 2026 · David Shusterman, MD

Appendix E: Stone Types and What They Mean

Stone analysis converts a generic diagnosis into a specific disease process. Whenever practical, retrieve a passed stone or a fragment removed during surgery and submit it for laboratory composition analysis. Appearance alone is unreliable, and mixed stones are common.

calcium oxalate

Calcium oxalate is the most common major component. Risk can be driven by low urine volume, high urinary calcium, high urinary oxalate, low citrate, high sodium intake, bowel disease, bariatric surgery, genetic factors, or combinations of these. Prevention typically preserves normal food-based calcium, pairs calcium with oxalate-containing meals, limits excessive sodium, avoids unnecessary high-dose vitamin C, and targets the abnormalities shown on metabolic testing.

calcium phosphate

Calcium-phosphate stones often occur in more alkaline urine. They may be associated with hypercalciuria, distal renal tubular acidosis, primary hyperparathyroidism, urinary tract anatomy, or medications such as carbonic anhydrase inhibitors. Excessive urinary alkalinization can increase calcium-phosphate supersaturation in selected patients, so pH goals require precision.

uric acid

Uric acid becomes poorly soluble in acidic urine. Low urine pH is often more important than total uric acid production and is frequently associated with insulin resistance, obesity, diabetes, chronic diarrhea, and high dietary acid load. Urine alkalinization can prevent uric acid stones and may dissolve selected radiolucent uric acid stones under medical supervision. Allopurinol is not automatically required for every uric acid stone.

Struvite and Infection Stones

Struvite stones form in the presence of infection with urease-producing organisms, which raise urine pH and promote magnesium-ammonium-phosphate crystallization. These stones may enlarge rapidly and form branching burdens. Treatment usually requires infection control and complete or near-complete stone clearance because residual infected material can support recurrence. Not every staghorn stone is struvite, and culture results may vary by sampling site.

Cystine

Cystine stones result from cystinuria, an inherited disorder of amino-acid transport. They often begin at a younger age and recur aggressively. Management emphasizes very high urine volume, sodium reduction, urine alkalinization, and, when necessary, cystine-binding medications under specialist monitoring. Family counseling and genetic evaluation may be appropriate.

Drug-Related and Matrix Stones

Some medications or their metabolites can crystallize directly, while others alter urine chemistry. Examples include selected antivirals, triamterene, sulfonamides, and medications that raise urine pH or lower citrate. Matrix stones contain a larger organic component and may be difficult to see on routine imaging. These uncommon stones require individualized evaluation rather than standard dietary advice.

The Clinical Translation

Calcium oxalate: investigate volume, calcium, oxalate, citrate, sodium, bowel absorption; prevention centers on dilution, normal meal-time calcium, sodium control, targeted citrate or other therapy.

Calcium phosphate: investigate high ph, hypercalciuria, renal tubular acidosis, medications; prevention centers on define cause, control calcium excretion, avoid indiscriminate over-alkalinization.

Uric acid: investigate persistently acidic urine, metabolic disease; prevention centers on raise urine ph, improve metabolic health, moderate purine excess when relevant.

Struvite: investigate urease-producing infection and residual stone; prevention centers on drain infection when urgent, clear stone burden, culture-directed management.

Cystine: investigate inherited cystine excess; prevention centers on high urine volume, sodium reduction, alkalinization, specialist medication when needed.

The stone is a specimen, not a souvenir. Its composition should influence the entire prevention plan.