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Types of Urinary Stones in Dogs

Updated: Jan 27, 2023

"If urate bladder stones or crystals are diagnosed in a dog that is not a Dalmatian, the dog should be tested for the presence of a liver shunt."

Uroliths are solid masses that form in the urinary tract. They are typically made up of mineral and acid salts, and can vary in size, shape, and composition. Other names of uroliths are calculi or also known as bladder stones, cystic stones, renal stones or kidney stones. Dogs are more likely to have stones in the bladder stones than in a kidney.

Uroliths only form when the minerals that make up the stones are present in adequate amounts for their crystals to combine and when crystals remain in the urine for an adequate length of time.

For some stones, the correct environment must also be present, such as the concentration or proper level of acidity. These various conditions can be affected by urinary tract infections, diet, digestion, the amount of urine that a dog produces, how frequently a dog urinates, medications, and genetics.

There are several types of urinary stones formed from various complexes of minerals but the three main types can be classified as:

1) struvite, 2) calcium oxalate, 3) urate stones and 4) cystine stones.

Like I said earlier, each type of stone develops only under very particular conditions. Let's take a look as some of the conditions for each type of urolith.

Struvite Stones

Struvite crystals are found even in normal urine. The majority of stones in dogs are this type of struvite stone and most of them occur in female dogs. Struvite is composed of magnesium, ammonium and phosphate. On on microscopic examination, the presence of struvite crystals alone do not require treatment. However, when struvite crystals are present as well as a bacteria-produced enzyme called urease, stone formation is possible.

The ammonium producing bacteria that are typically the ones responsible for producing the urease are Staphylococci (often called Staph) and Proteus bacteria.

"When the body breaks down amino acids, it must contend with ammonium that is generated in this process. The ammonium, which would be toxic if left alone, is converted to urea, which is much less toxic and is readily soluble in water making for its easy disposal in urine. Unfortunately, adding urease-positive bacteria into the urinary bladder converts the urea back into ammonium. The combination of infection and inflammation caused by the ammonium creates a matrix which traps the struvite crystals and gels into an actual stone. This reaction can only take place in an alkaline urine but the ammonium creates the perfect pH for stone formation. In dogs, the general rule is: No infection, no struvite bladder stone." ( from

Laser treatment and special diets can sometimes break up or dissolve struvite stones.

Calcium Oxalate Stones

Calcium oxalate stones are caused by an excess of calcium and oxalate in the urine. There's a strong hereditary component to forming calcium oxalate bladder stones (this is also true in humans). There is a substance (called nephrocalcin) in urine that naturally inhibits the formation of calcium oxalate stones. Both humans and dogs who form calcium oxalate bladder stones are found to be lacking in nephrocalcin so the production of defective nephrocalcin may be a genetic problem.

In humans, the genetic predisposition for stone formation is coupled with dietary issues (problem foods include spinach, peanuts, chocolate, dairy products, calcium supplements, vitamin C supplements, and tea). Dogs are more likely to eat the same commercial brand of dog food for every meal. They don't usually get the the variety of meals that humans eat which may sound boring but it also means that their diet can be used to manage the problem in the dog. Unless the dog is receiving an unusual treat supply, genetics (not diet) is the cause for calcium oxalate stones.

Calcium oxalate stones do not respond to dietary interventions. Vets will typically use interventions such as laser treatment or other treatment measures, sometimes even surgery, depending on the size of the stones.

Urate Stones

Urate bladder stones are most commonly the result of a genetic abnormality that causes a defect in the metabolism of uric acid. Urate stones are not as widespread in the general population of dogs. However, one of the most common uroliths in Dalmatians is composed of urate crystals.

Another situation that can cause urate urinary stones is liver shunts. In liver diseases such as portosystemic shunts, urate bladder stones may form if the urine is highly acidic or becomes extremely concentrated. In fact, it is generally believed that if urate bladder stones or crystals are diagnosed in a dog that is not a Dalmatian, the dog should be tested for the presence of a liver shunt.

Cystine Stones

Cystine is an amino acid that is normally reabsorbed by the kidneys. Cystine stones are caused by an inherited disorder that causes an excess of cystine in the urine. Breeds more likely to have these stones are Newfoundlands

  • Labrador Retrievers

  • Australian Cattle Dogs

  • Miniature Pinschers

  • Mastiffs

  • American Pit Bull Terriers

  • English Bulldogs

  • French Bulldogs

  • Chihuahuas

  • Rottweilers

  • Dachshunds

  • Scottish Terriers

Both males and females can have the genetic anomaly that causes the increased concentration of cystine but it's usually the males that will have problems from the formation of cystine stones due to their anatomy.

Diagnosis of Bladder Stones in Dogs

Vets can identify most bladder stones in dogs through an X-ray or abdominal ultrasound. Cystine stones won't show up on an x-ray and can be diagnosed by a vet with ultrasound or manual palpation in some cases.

Your vet will likely also want to submit urine for analysis and culture for bacteria. Because tumors and infections may cause the same clinical signs as bladder stones, it's important to follow all your vet's testing recommendations.

Treatment for urinary stones can vary depending on the type and size of the stones, but may include medication, dietary changes, or even surgery.

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