Bladder And Kidney Stones In Your Dog Or Cat
And What You And Your Veterinarian Can Do
Ron Hines DVM PhD
Our pets suffer from kidney and bladder stones (calculi or uroliths) similar to the ones that affect us. Most of these stones are composed of the mineral salts of the common elements found in our bodies and the things we eat: calcium, magnesium, ammonia, phosphorus and carbonates.
Several things contribute to the formation of urinary tract stones in dogs and cats. (cats go here) However, why they affect one cat or dog and not another is not understood. These minerals are present in moderate amounts in the urine of all animals. However, if the concentration of mineral salts are too high in the pet’s urine, they will crystallize and precipitate out, layer upon layer. This can occur in the kidneys or farther down the tract in the dog or cat’s bladder. The urine of pets should naturally be acidic. Most mineral salts are less soluble in alkaline urine so any factor that make your pet’s urine more basic or alkaline contributes to stone formation.
Many bacteria have the ability to decompose urea, a natural constituent of your pet’s urine, into ammonia. In doing so, they raise the pH of the urine “alkalinizing” it. When that occurs, crystals of the mineral salts come out of solution. Small objects, such as cellular debris or bacteria, give those crystals an opportunity to form layer-upon-layer on the debris which eventually become a stone or calculus. Certain breeds and lines of dogs are susceptible to stones of a different composition. Those stones are formed because uric acid, a byproduct of protein metabolism, occurs in their blood in too high a concentration. The best-known example of this are the ammonium urate stones sometimes formed by Dalmatians. (read here)
Other dogs and cats are thought to be born with mucosal immunity defects (decreased resistance to infections) that leave them more susceptible to urinary tract infections that can lead to urinary track stones.
The two most common signs of bladder stones are blood in the urine and painful, frequent attempts to urinate. Blood in the urine (hematuria) occurs when stones irritate and traumatize the sensitive lining of your pet’s bladder. The inflamed bladder lining is also quite painful – particularly when small sand-like stones and grit manage to pass out with the urine. That irritation causes pets with bladder stones to attempt to urinate much too frequently. They will squat and strain with no apparent success or with just a few drops produced. The urine passed may be red or port wine in color, or it may appear perfectly normal. In between urination dogs and cats with urinary tract issues are often restless. Dogs might walk with their loins down and in a crouched position. Cats often spend an unusually long periods in their litter boxes or begin to pee in exotic locations. They might lick their genitals more frequently. Pet owners might misinterpret these signs as signs of constipated. When the abdomen of these pets are palpated, your veterinarian can often detect small hard stones in their bladder. When gently pressed together, these stones typically grind like a handful of marbles. Large solitary stones in the bladder are also quite hard to miss.
If your veterinarian does not attend to this problem immediately, one of the stones might lodge and block your pet’s urethra, the tube leading from its bladder to its penis or vagina. When this happens, urine will back up into the bladder and eventually increase pressure within its kidneys to dangerous levels. The end result can be kidney failure and uremia, depression and vomiting. Your pet’s bladder ,when it cannot expel urine can stretch to several times its normal size. At some point, it may even burst. It might take weeks after your veterinarian unblocks your pet for its bladder’s tone and size to completely return to normal.
A blood sample taken from an obstructed dog or cat might have an elevated urea (BUN) and creatinine content depending on how long the obstruction has existed. Despite those changes, dogs and cats with stones do not typically run high fevers. Analysis of the urine of these pets usually finds that it contains blood and white blood cells. (read here & here) When a urinary tract infection reoccurs frequently in your dog or cat, it should always be checked carefully for the undetected presence of bladder or kidney stones. Some can be quite difficult to visualize in x-rays, other types are quite obvious. These stones are porous and bacteria can reside within them where antibiotics and your pet’s immune system cannot easily reach and destroy them. Somewhat less common in pets are stones that form higher up the urinary track in its kidneys. Those stones can cause sudden colic and intermittent bloody urine, or they may occur without any visible symptoms at all. Occasionally, stones will leave the kidney and lodge and plug up one of the two ureters, the tubes that lead to the bladder. This event is marked by severe pain, agitation and straining until the stone has passed or has been surgically removed.
Enemas are often required before urinary tract x-rays. When that is done, most stones of the common compositions are quite visible on x-rays. Occasionally, certain stones contain more organic material than mineral, so they are difficult or impossible to visualize. If your veterinarian suspects that form of stone, the vet might fill your pet’s bladder with air or radiopaque dye before the x-ray is taken. Ultrasound will also detect these radio-lucent (do not appear on x-rays) stones.
As I mentioned at various ponts in this article, true bladder or kidney stones are exceeding rare in cats (go here) but much more common in dogs. When bladder or kidney stones are large and unlikely to plug your pet’s ureters or urethra, your veterinarian might attempt to manage them medically through a special diet. To do so, your veterinarian would first want to know what the stones were composed of. Struvite-based stones (magnesium ammonium phosphate or triple phosphate) are the most common of the urinary tract stones. Schnauzers and dachshunds seem particularly susceptible to struvite stones. Struvite crystals have a characteristic microscopic shape in the urine. (see here) Specialty diets are available that encourage these stones to slowly dissolve. These diets have less protein, so less ammonia is formed in the urine. They also contain less magnesium and phosphorus, the building blocks of struvite. Since struvite dissolves in acidic urine, these diets contain ingredients to keep the urine acidic. A common trade name for one of these diet is s/d™. There are many competing brands. If the stones have not dissolved completely in a few months they probably need to be removed surgically. I don’t believe that dogs should be left on these ultra low-protein foods for more than 5 months. Cats can stay on these diets perhaps a month or so longer. For oxalate-based stones, the company recommends their c/d brand. For urate or cysteine based-stones, their u/d brand.
In female dogs, veterinarians are sometimes able to reach up into the pet’s bladder from the vagina and crush small stones with a medical instrument called a biopsy punch. This approach requires the use of a fluoroscope. It is not appropriate for toy breeds or cats. But in many more cases, the pet’s bladder is opened through an incision at its thickest point and the stones and grit are manually scoop out. A catheter is usually passed out through the urethra and left in place to be sure no small residual stones or “sand” block the urethra during healing. When a stone is present in the urethra or in the ureter, moving it back into the bladder or kidney and remove it from there is usually the safest option. That is to prevent strictures (scars) from forming in the urethra or ureters that narrow the tube’s. diameter. Yag lasers have also been used to successfully destroy urinary tract stones in dogs and cats without the need for surgery. (read here)
All urinary tract stones should be sent to a specialized veterinary laboratory for analysis. All stones are less likely to form if your pet has free access to water and frequent opportunities to urinate. If Hydra Care® will increase your pet’s water consumption enough to prevent urinary tract stones is something we have not yet determine. The mineral crystals that form stones are less likely to come out of solution in dilute urine. Eliminating bacterial urinary tract infections and checking the bacteria’s antibiotic sensitivity when found, performed twice a year might help as well.
Adding salt (NaCl) to your dog or cat’s water or food is not a good idea. It will not encourage them to drink more or make urinary tract stones less likely to reoccur. Contrary to what was once thought, salty foods do not encourage thirst – they do the opposite. (read here & here) Diets high in grain and vegetables tend to produce alkaline urine, which allows certain stones to form.
Calcium Oxalate stones seem to be getting more common and can be very frustrating for veterinarians to treat. They differ from struvite stones in that they form in acidic urine (read here & here). Unfortunately, they are harder to prevent through dietary manipulation than struvite or urate calculi (stones) are. As a result, these stones must be removed surgically once they have formed, and they often reoccur within a few years despite treatment. They are more common in male dogs (75%) and Burmese, Himalayan and Persian cats. The most common dog breeds affected by oxalate stones are Yorkshire terriers, poodles, shih tzus, schnauzers, lhasa apsos and bichon frises. These stones appear to be associated with excess calcium in their blood stream and urine. Sometimes these stones are the result of other diseases such as Cushing’s disease or the excessive administration of corticosteroid medications.
Many mineral salts are naturally excreted into urine at concentrations greater than at which they would normally fall out of solution in a beaker of distilled water. That is called supersaturation. In those situations, a substance called nephrocalcin, produced by the kidneys, inhibits stone formation. When too little of this compound is present, it is thought that oxalate stones may result. (read here) How this might apply to dogs and cats is unknown. Supplementing your pet’s diet with oral potassium citrate, given twice a day, is also thought to lessen the probability of calcium oxalate stone reformation.
