Kidney stones in dogs and cats: what owners need to know

Kidney stones (nephroliths) in dogs and cats are rare and usually cause no symptoms. Complications such as infections and urinary obstructions can potentially put kidney health at risk. When symptoms are present, they can include frequent urination, abdominal pain, blood in urine, vomiting, lethargy, and loss of appetite. If you have a dog or a cat, read on to learn:

• How kidney stones form
• Symptoms of kidney stones
• How kidney stones are diagnosed and treated

Not all kidney stones require veterinary care. The treatment for kidney stones in cats and dogs will vary depending on the location and size of the stones, the type of stones, and if there is an infection or obstruction present. Struvite and calcium oxalate stones are the most common nephroliths in dogs and cats. Struvites can sometimes be dissolved with a special diet, but calcium oxalate stones cannot be dissolved and require different treatment methods.

Kidney stones, or nephroliths, are clumps of minerals that form rocklike formations in the kidneys large enough to see with the naked eye. Minerals can separate out of urine under specific conditions. These minerals cluster together over time to form microscopic crystals and larger stones, more commonly in the lower urinary tract. There are many contributing factors for stone formation in dogs and cats, such as:

• pH of urine
• Nutritional factors
• Urinary tract infection
• Urine concentration
• Individual metabolic abnormalities
• Genetics

Some kidney stones are small enough to easily pass through the urinary tract, while others stay in the kidneys without affecting an animal’s health. Stones can become lodged in the ureters, the small tubes that transfer urine from the kidneys to the bladder, and cause a urinary blockage. Urinary blockages stop the normal flow of urine through the urinary tract and quickly lead to kidney damage.

How common are kidney stones in dogs and cats?

“Kidney stones are rare in dogs and cats,” explains Dr. Jo Myers, a veterinarian on the Vetster platform. “Urinary stones are far more likely to develop in a dog or cat’s bladder.” Stones in the ureters are more common in cats than in dogs. A cat’s ureters are narrower and are more likely to become obstructed.

Symptoms of kidney stones in dogs and cats vary depending on size, location, number of stones in the kidneys, and the presence of infection or ureteral obstruction. Urinary stones in the kidneys are usually asymptomatic unless the kidneys become irritated and inflamed or stones get lodged in a ureter and block the flow of urine. Many stones in the kidneys are incidental findings, meaning they are not causing symptoms and are discovered unintentionally when a vet is testing for something else. Urinary tract stones can almost always be seen on abdominal radiographs and ultrasounds.

If a dog or a cat has kidney stones, their symptoms may include:

• Abdominal or back pain
• Bloody urine
• Painful urination
• Increased thirst
• Excessive or frequent urination
• Vomiting
• Lethargy
• Loss of appetite

Struvite kidney stones are more likely to form when there is a bacterial infection that alters the pH of the urine. A bacterial kidney infection (pyelonephritis) often causes appetite loss, vomiting, and pain in the abdomen. In addition, stones can damage the lining of the urinary tract and lead to urinary tract infections. Stones that become lodged in the ureters often cause significant abdominal or back pain. When a ureter is blocked, urine backs up in the connected kidney, leading to kidney damage. Signs of kidney dysfunction are generally not obvious until at least two-thirds of the kidney is destroyed. As a result, clinical signs of a ureteral obstruction may not be seen until:

• Both ureters are obstructed
• The patient has chronic kidney disease
• A kidney infection develops

If only one ureter is blocked, there may not be any detectable symptoms as the other kidney could be working properly.

Stones in the kidneys can usually be seen on an abdominal ultrasound or X-ray. They may be seen when a vet takes diagnostic images for another health issue or during a wellness exam as an incidental finding. If a patient has urinary symptoms and kidney stones are suspected, an X-ray with contrast added to the urine helps a vet to fully characterize the stones and determine the treatment plan. Additional diagnostic tests may involve:

• Urinalysis
• Urine culture
• Blood tests
• Stone analysis

The presence of infection, chemical composition of the stones, and presence of a urinary tract obstruction will affect how kidney stones are treated in dogs and cats. There are many types of stones that can form in the kidneys, but struvites and calcium oxalates are the most common.

Medical treatment of kidney stones varies based on stone size, location, number, type, and if any complications are present, such as infection or obstruction. Stones that are not causing symptoms or presenting any risk for obstruction usually do not require treatment. When indicated, treatment may include:

• IV fluids and diuretics to encourage stones to pass
• Placement of a stent to bypass a lodged stone in the ureter
• Dietary therapy
• Antibiotics for concurrent bacterial infection, if present
• Pain medication
• Surgery
• Lithotripsy

If a kidney is significantly damaged due to infection or obstruction, it may require surgical removal. Depending on the mineral composition, a urinary diet may be able to dissolve a kidney stone. Special diets are also used to prevent the formation of more stones in the future. Dissolving kidney stones with a therapeutic diet can take multiple weeks. Only struvite stones can be dissolved. However, calcium oxalate stones are the most common type of kidney stone in cats, and they cannot be dissolved. Stones that cannot be dissolved through a diet change require more invasive treatment options such as lithotripsy or surgical intervention. No matter the chosen treatment, a vet may recommend follow-up testing to ensure the treatment is successful.

Urinary symptoms, vomiting, abdominal and back pain, and lethargy are common symptoms of many different medical conditions. Diagnostic testing with a veterinarian is needed to identify the underlying cause of the symptoms. Kidney stones are rare in dogs and cats, so these symptoms are more likely to be caused by another issue. It’s important for dog and cat parents to talk to a veterinarian whenever they notice changes in their pet’s physical health or normal behavior. If your dog or cat has had urinary stones in the past and is exhibiting symptoms, talk to a vet for treatment and long-term care. If you have questions about your dog’s or cat’s symptoms or risk of urinary stones, online vets are available for virtual visits through the Vetster platform.

How do you treat kidney stones in dogs?

Not all kidney stones require treatment. If a stone is causing symptoms or is at risk for obstructing a ureter, treatment options may include a dissolution diet, surgical removal of the stone, placing a stent in the ureter to bypass a lodged stone, or a lithotripsy procedure to break up larger stones so they can pass. The treatment plan will vary based on the size, chemical composition, and location of the stone, as well as whether there are any complications such as infection or urinary obstruction.

How long does it take to dissolve kidney stones in dogs?

It usually takes around eight to twelve weeks to dissolve struvite stones with a specialized diet. If a dog’s stones need to be removed quickly, another treatment option may be needed. Struvite stones are the only stone type that can be dissolved with diet. Calcium oxalate stones cannot be dissolved and require another treatment option.

Can cat food cause kidney stones?

Diet plays a large role in the development of urinary stones in cats. However, cat food alone does not cause kidney or bladder stones, and there is no specific cat food that is directly linked to the formation of kidney stones. Urinary stones only form when certain conditions within the urine are met, including the amount of minerals present in a cat’s body from their diet.