The five types of kidney stones are calcium oxalate, calcium phosphate, uric acid, struvite, and cystine. Calcium oxalate stones are by far the most common, making up the majority of cases, while cystine stones are the rarest. Each type forms under different chemical conditions in the urine, which means prevention and treatment look different depending on which kind you have.
Calcium Oxalate Stones
Calcium oxalate is the most frequently diagnosed kidney stone, and it forms when calcium binds with oxalate in urine that’s too concentrated or too acidic. Several factors raise your risk: low fluid intake, high-oxalate foods, and even certain antibiotics that kill off gut bacteria responsible for breaking down oxalate before it reaches your kidneys.
Foods especially high in oxalate include spinach, rhubarb, nuts and nut products, peanuts, and wheat bran. You don’t necessarily need to eliminate these entirely, but reducing them can lower the oxalate concentration in your urine. Interestingly, getting enough calcium from food actually helps, because dietary calcium binds to oxalate in the gut and prevents it from being absorbed into the bloodstream.
If you’ve had recurrent calcium oxalate stones, a 24-hour urine collection can measure how much calcium and oxalate your body is excreting. Normal urinary calcium is below 250 mg per day for men and below 200 mg per day for women. Oxalate should stay below about 40 mg per day. When these values run high, targeted dietary changes or medications that reduce calcium in the urine can cut recurrence significantly.
Calcium Phosphate Stones
Calcium phosphate stones are chemically distinct from their oxalate cousins. They form in alkaline urine rather than acidic urine, which means the underlying conditions driving them are different. People taking certain medications, particularly a class of drugs used for conditions like glaucoma and altitude sickness, are at higher risk. These medications create a paradox: they cause mild acid buildup in the blood while simultaneously making the urine more alkaline, reducing citrate (a natural stone inhibitor), and increasing calcium excretion.
Treatment overlaps somewhat with calcium oxalate stones. Medications that lower urinary calcium are effective for both types. For people with low urinary citrate, citrate supplementation is particularly important because citrate is a potent inhibitor of calcium phosphate crystal formation.
Uric Acid Stones
Uric acid stones account for a smaller but significant share of kidney stones, and they’re closely tied to metabolism. Uric acid is a waste product from the breakdown of purines, compounds found in red meat, organ meats, and shellfish. When urine is both highly concentrated and acidic (typically below a pH of 5.5), uric acid stays in its non-dissolved form and crystallizes.
The connection to insulin resistance is important. People with type 2 diabetes or metabolic syndrome tend to produce more acidic urine, which is why uric acid stones are more common in these groups. Low fluid intake compounds the problem by keeping uric acid concentrated.
The good news is that uric acid stones are among the most treatable. Raising urine pH to around 6.0 with a citrate supplement can dissolve existing stones and prevent new ones. This is the only common stone type where dissolution without a procedure is reliably possible. Drinking enough fluid to produce over 2 liters of urine per day also helps keep uric acid from crystallizing.
Struvite (Infection) Stones
Struvite stones are made of magnesium ammonium phosphate, and they don’t form from diet or metabolism. They form because of urinary tract infections caused by specific bacteria that produce an enzyme called urease. This enzyme breaks down urea in the urine into ammonia, which raises the pH and makes the urine alkaline. In that environment, struvite crystals grow rapidly.
These stones are dangerous because they can grow very large, sometimes filling the entire kidney and forming what’s called a “staghorn” stone. They tend to develop more often in women (who get UTIs more frequently) and in people with structural abnormalities of the urinary tract or those who use catheters long-term.
Treatment almost always requires removing the stone, because as long as infected stone material remains, the infection is difficult to fully clear. Antibiotics alone won’t resolve the problem. In some cases, a medication that blocks bacteria from producing ammonia can slow or stop stone growth, but stone removal is the primary goal.
Cystine Stones
Cystine stones are the rarest of the five types and are caused by an inherited genetic condition called cystinuria. The condition follows an autosomal recessive pattern, meaning a person needs to inherit a faulty gene copy from both parents. These genetic mutations affect the kidneys’ ability to reabsorb an amino acid called cystine, so it builds up in the urine and forms crystals.
Because this is a lifelong genetic condition, most people with cystine stones experience their first episode during adolescence or early adulthood. Recurrence is common and often requires ongoing management throughout life.
The primary strategy for preventing cystine stones is raising urine pH to around 7.0 with citrate supplements, which makes cystine more soluble. High fluid intake is especially critical for cystine stone formers, as diluting the urine is one of the most effective ways to keep cystine from crystallizing. Some people need additional medications that bind to cystine and make it more soluble when dietary and pH adjustments aren’t enough.
Rare and Drug-Induced Stones
Beyond the five main types, a small number of kidney stones are caused by rare genetic conditions or medications. Xanthine stones, for example, result from hereditary xanthinuria, a condition where the body can’t convert xanthine (an intermediate product of purine breakdown) into uric acid. Xanthine accumulates in the kidneys and forms crystals. People with this condition have very low uric acid levels in their blood and urine, which is the opposite of what you’d see in uric acid stone formers.
Certain medications can also crystallize in the urine and form stones. These drug-induced stones are uncommon but worth knowing about if you take medications long-term, particularly some older antiviral drugs.
Prevention That Applies to All Stone Types
Regardless of which type of stone you’ve had, fluid intake is the single most universal prevention strategy. Drinking enough to produce more than 2 liters of urine per day, which generally means consuming about 2.5 to 3 liters of fluid daily, reduces the risk of recurrence by roughly 45%. The American College of Physicians specifically recommends this target for anyone who has had a kidney stone and currently produces less than 2 liters of urine per day.
Beyond fluids, knowing your stone type matters enormously. If you’ve passed a stone, saving it for analysis gives your doctor the information needed to tailor dietary and medical prevention. A 24-hour urine collection can identify the specific chemical imbalances driving your stone formation, whether that’s excess calcium, low citrate, high oxalate, or overly acidic urine. Without this information, prevention is essentially guesswork. With it, recurrence rates drop substantially.