Kidney stones form in dogs for a few different reasons. The different causes ultimately predict which type of nephro (kidney) + lith (stone) is most likely to form. And the type of stone affects what treatments might help. Dogs with small kidney stones really may show no signs at all. Kidney stones may show up on x-rays of the belly that are being taken for unrelated reasons, as a so called “incidental finding.” For instance, they may be discovered when you think your pooch may have eaten something he shouldn’t have, like one of your favorite earrings. (Your vet found a stone, all right, but not the missing diamond you were seeking.) Since kidney stones don’t seem to cause dogs as much pain as they do for people, why worry about them at all?
Why are kidney stones in dogs important?
A kidney stone that allows normal urine flow out may be one that your vet watches closely, but ultimately leaves untreated. However, if the stone gets very large, or if little pieces break off and lodge in the ureter (the long narrow tube that connects each kidney to the urinary bladder) it becomes a ureterolith, and is likely very painful. Kidney colic, signaled by abdominal pain, discomfort and even vomiting, may result; the kidney may also swell and become damaged. If this should happen simultaneously to each kidney, and the blockage persists, your dog will likely become critically ill from the disrupted flow of urine. For these reasons, if you think your pet’s abdomen is painful, or his urinations change in any way, please contact your vet right away. A urinary obstruction is a life threatening emergency that must be treated!
Signs of kidney stones in dogs
The signs and symptoms of kidney stones could include:
- Fever
- Abdominal discomfort
- Kidney pain
- Blood in the urine (hematuria)
- Altered urine production (increased or decreased)
- Lethargy
- Poor appetite
- Vomiting
- Weight loss
Causes and types of kidney stones
Metabolic kidney stones, those stones formed due to some blood or urinary imbalance, are a bit more common in dogs than are stones caused by infection1. Female dogs outnumber males when it comes to stones2, and there are certain dogs and certain dog breeds that seem to be “stone formers.” They may form stones multiple times, despite ordinary precautions being taken to prevent them. Calcium oxalate is one of the most common types of kidney stones, and is common in the bladder, too.
Stones that form in the bladder or kidney because of chronic bacterial infection are usually struvite. The stone components are magnesium, ammonium and phosphate.
Some dog breeds with an increased risk of kidney stones are listed here2:
Diagnosis of kidney stones
Struvite and oxalate stones usually show up readily on plain radiographs, but small stones may be hidden by whatever else is in your dog’s belly. Certain stones don’t consistently image well either, especially urate stones, which are common in Dalmatian dogs, so simple x-rays may not give enough information. Once it’s found, predicting the stone type is challenging, so your vet will need some diagnostic aids to help with that. She will want to do some tests to see what impact the stone(s) may be having on your dog’s kidney health, and whether other conditions may be present that might increase the risk of stones.
If a kidney stone is suspected, or already diagnosed, your vet will likely want to have a minimum data base to start from, consisting of these tests:
- Complete blood count (CBC)— Low red blood cells (anemia) or high white blood cells are important findings
- Blood chemistry with electrolytes— Testing for evidence of kidney disease and risk factors for stone formation
- Urinalysis— The urine quality may predict kidney disease and help identify white blood cells and red blood cells that suggest bacterial infection, or crystals that may help predict stone type
- Urine culture with susceptibility— Identifies bacterial infection and best antibiotic choice(s)
- Abdominal radiographs (x-rays)— to examine the size and shape of the kidneys and look for urinary stones
- Systemic blood pressure— To identify an important complication of kidney disease
Additional tests that may be suggested:
- Abdominal ultrasound— This will help verify the location of any stones and the suspected degree of any obstruction
- Contrast radiography— Dye studies may be needed to confirm blockage and help to show the contribution that each kidney makes to urine production
Treatment of kidney stones
Even if complications of kidney stones are not obvious, their presence may contribute to the progression of chronic kidney disease (CKD). Since oxalate stones do not dissolve, treatment can be challenging for your pet and for your veterinary team.
Some urinary stones, your veterinarian may want to treat conservatively, with a combination of antibiotics, diet, and plenty of water. Dissolving kidney stones completely, often takes months, but any early reduction in size is a good start.
Medical efforts to dissolve kidney stones are usually safer than surgery, but won’t work for all stones. Skilled surgery is widely available, but does risk permanently damaging the affected kidney, even if the surgery goes smoothly. Veterinary urologists can offer special techniques to break stones into smaller pieces so they can just pass out in the urine. This alternative procedure to surgery could offer a safe cure for kidney stones3.
For bigger stones, specialists might break them up from the inside using endoscopes and special tools. It’s always fair to ask your doctor if a recommended surgery is the only option, or if there might be a cutting edge technology to try, instead.
Monitoring and Management of kidney stones
If your vet suspects oxalate kidney stones, she may suggest using diet and some medications to reduce or slow stone growth, with a significant emphasis on increasing water intake. A general strategy involves reducing mineral concentration to discourage crystal and stone formation. Increasing water intake makes the urine more dilute and should reduce the amount of mineral available to form a stone. A variety of diets have been used successfully to prevent or manage urinary stones, but finding the best fit for your dog could take some trial and error. These strategies are worth the effort, for sure, to try to avoid the pain and problems that a growing kidney stone may cause. If an underlying cause for stones is suspected, then resolving that problem will be another important way to protect those kidneys from more stone damage.
Even if the stones don’t seem to be active or causing infection or blockage, regular monitoring of lab tests for kidney function and urine quality will continue to be important for the rest of your dog’s life. Your vet will want to make sure that the prevention strategy is working, to see that the stones are not growing or causing complications. That evaluation will likely need some form of imaging rechecks, with either radiographs (x-rays) or ultrasound. If the stones were removed or treated medically, monitoring for their recurrence will be key to keeping your dog healthy. You and your veterinarian can determine the monitoring schedule that best matches your dog’s condition. A stone-free dog is a happier and healthier pet.
If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.
Resources:
- Low WW, et al. Evaluation of trends in urolith composition and characteristics of dogs with urolithiasis: 25,499 cases (1985–2006). J Am Vet Med Assoc. 2010;236:193–200.
- Jessica E Markovich and Mary Anna Labato, Medical Management of Nephroliths and Ureteroliths in JD Bonagura and DC Twedt ed Kirk’s Current Veterinary Therapy XV, Saunders Elsevier, St. Louis, 2014 PP 892-896.
- Berent, Chick Weisse Interventional Strategies for Urinary Disease in Kirk’s CVT XV JD Bonagura dn DC TwedtElsevier Saunders St Louis 2014 PP884-892
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