Bladder Stones in Dogs: An Overview

Dog Breeds

Bladder stones are, like their name, stones which can form in the bladder of dogs. Although they are more common in older dogs, even pets under a year of age can develop bladder stones. These stones can travel into the urethra and get lodged causing a urinary tract obstruction, and in some rare cases can form in the kidneys.

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Definition of Bladder Stones

Bladder stones are abnormal accumulations of minerals and other substances in the urinary bladder that congregate to form what we commonly refer to as “stones.” Stones usually occur in the hollow organs of the body or in their passages, such as the urinary bladder, kidneys, gall bladder, ureters or urethra. These stones are generically called “calculi.” When they are in the urinary tract, they are called “uroliths.” For our articles, we will just call them stones, as they can be formed in the kidneys, bladder, gall bladder or elsewhere. Stones can occur in any part of the urinary tract, from the kidneys to the ureters to the urinary bladder and ultimately to the urethra. They become problematic when they obstruct the ureters (the passages between the two kidneys and the urinary bladder) or the urethra (the single passage from the urinary bladder to the outside world). When this happens, the stones block the normal outflow of urine – a condition that is extremely painful and can rapidly become life-threatening if not treated immediately. In dogs, urinary stones are most commonly formed in the bladder and then become stuck in the urethra.

Causes of Bladder Stones in Dogs

Canine urine contains a number of different minerals, or salts, that normally remain dissolved in fluid. When the urine becomes too concentrated, or “supersaturated,” these dissolved salts can precipitate out of the fluid to form solids in the form of crystals. These crystals can damage the lining of the urinary tract, causing blood in the urine (hematuria), and can predispose affected dogs to developing bacterial urinary tract infections. Over time, the mineral crystals can aggregate with organic material (which can include bacteria) and coalesce to form calculi, or what commonly are called stones. When calculi form in any part of the urinary tract, they are referred to as uroliths. For the purpose of our articles, we are going to refer to calculi, and uroliths, as stones. The pH of urine contributes to stone formation. Some crystals form in urine that has a high pH (alkaline urine), while others form in acidic urine, which has a low pH. Urine pH can be affected by a number of things, including diet, hydration, the presence of bacteria/urinary tract infections, certain medications, conformation of urinary tract structures and genetics. Common types of urinary tract crystals and stones are struvite (magnesium ammonium phosphate), calcium oxalate, urate, calcium phosphate, silicate and cystine. The crystals can accumulate to form one stone, many stones, small stones or very large stones, and the surface of these stones can range from smooth to jagged.

Prevention of Bladder Stones

Any obstruction of the canine urinary tract is potentially fatal. A well-balanced, high-quality diet can promote urinary tract health. Annual veterinary check-ups, including routine blood work and urinalyses, can help veterinarians detect abnormal levels of crystals in the urine well before they become symptomatic or form stones. Once detected and removed, stones are best prevented (or at least managed) by dietary changes, including a protein-restricted diet. There are a number of good, commercially available diets to address problems with stone formation and other urinary tract problems. It is also important to keep dogs well-hydrated, because dehydration increases the concentration of canine urine and predisposes the dog to developing crystals and urinary stones.

Special Notes

Urinary tract infections predispose dogs to development of stones in their urinary tracts. The reverse is true as well, underscoring the importance of annual veterinary examinations accompanied by urinalyses and routine blood screening for our companion animals.

Symptoms and Types