Visit Your Vet: What is a Urinary Stone?

Catherine Lenox, DVM, CVA, Diplomate ACVN

Manager of Scientific Affairs, Royal Canin USA

Urinary stones are commonly diagnosed in cats and dogs, but many people do not know what they are or what to expect before or after diagnosis. Urinary stones are essentially clusters of minerals that form in the urinary tract. Examples of minerals that can contribute to urinary stones include calcium, magnesium, and phosphate. Minerals in the urine bind together in the form of crystals or stones. Stones are larger and more solid than crystals.

What Happens When a Urinary Stone Forms

Urinary stones are also called calculi or uroliths. In pets, urinary stones may be found in the kidney, ureter, bladder or urethra. Stones found in the kidney are typically called nephroliths, and bladder stones can also be called cystoliths or cystic calculi. Because the ureter and urethra are narrow tubes through which urine passes, stones in these parts of the urinary tract are the most dangerous.  These stones can cause blockage of urine flow when they are the right size to obstruct the ureter or urethra. In those cases, the pet becomes suddenly sick due to kidney failure and/or the inability to urinate.  If you notice a loss of appetite, straining, vomiting, or signs of pain or discomfort, take your pet to your veterinarian or a veterinary emergency clinic immediately, as this can be a life-threatening complication.

Clinical Signs of Urinary Stones

In addition to the serious signs associated with urinary obstruction, urinary stones can cause more mild clinical signs in cats and dogs, including:

  • Blood in the urine
  • Straining to urinate
  • Urinating small amounts more frequently
  • Inappropriate urination outside the litter box
  • Urination inside the house with a normally well house-trained dog
Sometimes, urinary stones may be associated with urinary tract infections, which can intensify clinical signs.

When Urinary Stones Form

Urinary stones form when the minerals contributing to stone formation build up in the urine. Oversaturation results in minerals binding together to form crystals and/or stones, and in some cases, the urine also contains promoters or lacks normal inhibitors, leading to an increased risk of crystal and stone formation.

Urinary stones are typically identified by a veterinarian using x-rays or abdominal ultrasound. Sometimes, pets may not show any outward physical signs of pain or difficulty urinating, but some cats and dogs with urinary stones may experience a great deal of pain or have one of the signs listed above. The two most common forms of urinary stones, struvite (magnesium ammonium phosphate) and calcium oxalate, can be seen on x-rays unless they are very tiny.

Tests for Pets with Urinary Stones


  • Abdominal Ultrasound: In some cases, tiny urinary stones or stones that are not seen on x-ray due to their density (usually one of the more rare types of urinary stones such as urate) are seen using ultrasound.

  • Urinalysis: Your veterinarian will also likely perform a urinalysis, which looks for infection, crystals and other signs associated with urinary stones.

  • Urine Culture and Sensitivity: Your veterinarian may perform a urine culture and sensitivity test. This helps identify infections in terms of the specific bacteria involved and the antibiotics that can be used to treat the infection. Struvite stones are more commonly associated with urinary tract infection in dogs, but not in cats. Calcium oxalate stones are rarely associated with infection.

  • Urinary Stone Treatment: When a stone is identified, it is not always possible to determine the exact mineral composition unless the stone is sent out to a lab for analysis. Sometimes the urinalysis will show crystals, but that does not always identify the stone type. Different urinary stones are often treated differently. Surgery may be necessary if your pet has a urinary stone.  Pure struvite stones can sometimes be dissolved with diet, while calcium oxalate stones cannot be dissolved.  For calcium oxalate stones, and other more rare types of stones, surgery or an endoscopic technique may be necessary to remove the stone.

Post-Care Dietary Considerations

After stone removal for any stone type, the veterinarian will likely recommend diet modification. For most patients, a veterinary therapeutic diet is recommended regardless of the stone type, as urinary stone prevention diets are not available over the counter.  There are different diets that help control and prevent different types of stones. The appropriate veterinary therapeutic diet will change the mineral composition of urine and increase water consumption to dilute the minerals in the urine, making them less likely to aggregate and form stones.

Be sure to ask your vet how Royal Canin diet options can help you care for a pet with a urinary stone.

VISIT YOUR VET

Remember that only your veterinarian can perform testing to properly identify, diagnose and prescribe the best treatment plan to manage urinary stones in your pet.

TIPS TO TAKE AWAY

  • Urinary stones form when the minerals contributing to stone formation build up in the urine. 
  • Urinary stones are typically identified by a veterinarian using x-rays or abdominal ultrasound. 
  • After stone removal for any stone type, the veterinarian will likely recommend diet modification.