Bladder And Kidney Stones In Dogs And Cats

Both dogs and cats suffer from kidney and bladder stones (calculi or uroliths) very similar to those found in humans. Most of these stones are composed of the mineral salts of common elements found in the body, calcium, magnesium, ammonia, phosphorus and carbonates. Their composition and consistency are similar to that of limestone.

Several factors contribute to the formation of urinary tract stones. If the concentration of mineral salts are too high in the urine, they precipitate out, layer upon layer, in the kidneys or farther down the tract in the bladder. The urine of dogs and cats should be naturally acidic. Most mineral salts are less soluble in alkaline urine so any factors that make the urine more basic or alkaline contribute to stone formation. Many bacteria decompose urine urea into ammonia and so alkalinize the urine. Like pearls, mineral salts come out of solution easier if they have a small object to attach to. That is why the debris of urinary tract infections often serve as foci for forming stones. Specific breeds and lines of dogs are susceptible to stones of different compositions. These stones are formed from the salts of amino acids and urates that occur in the blood of these dogs in too high a concentration. The best-known example of this are the ammonium urate stone formed by Dalmatians. To this day we do not know why some dogs form bladder and kidney stones and others do not. Dehydration increases the concentration of minerals within the urine and can increase stone formation. Female animals of all species are more susceptible to urinary tract infections and subsequent stones due to their shorter urethra. Other dogs and cats are born with mucosal immunity defects that leave them more susceptible to urinary tract infection.

The two most common signs of bladder stones are blood in the urine and painful urination. Blood in the urine or hematuria occurs when stones irritate the bladder’s sensitive lining causing bleeding. The inflamed bladder lining is quite painful as are the small sand-like stones that pass out with the urine. Dogs with bladder stones attempt to urinate much too frequently. They will squat and strain with no apparent success. The urine may be red or port wine in color. When they do urinate, the quantity of urine is small. In between urination these pets are restless. They walk with their loins down in a crouched position. Owners may misinterpret these signs and assume the pet is constipated. When I palpate the abdomen of these animals I can often feel small stones in the bladder grinding together like marbles. Large solitary stones in the bladder are hard for me to miss. If a veterinarian does not attend to this problem immediately, one of the stones may obstruct the urethra, the tube leading from the bladder to the penis or vagina. When this happens, urine backs up into the body causing uremia, depression and vomiting. The bladder stretches to several times it normal size and may even burst. It may take weeks after the problem is relieved for the bladder’s tone and size to return to normal. Blood taken from obstructed animals has elevated urea and creatinine and its ionic balance is disrupted. Despite these changes, dogs and cats with stones do not run high fevers. Analysis of the urine of these pets usually finds blood and white blood cells. Bacteria may also be present in the urine. Any urinary tract infection that reoccurs frequently should be checked carefully for the presence of bladder or kidney stones. These stones are porous and bacteria reside within them where antibiotics and the body’s immune system cannot easily reach them. That is why infections frequently reoccur.

Somewhat less common are stones that form in the kidneys. These stones may cause sudden colic and intermittent bloody urine or may occur without any visible symptoms. Occasionally, stones will leave the kidney plugging the ureters, the tubes that lead to the bladder. This event is marked by severe pain, agitation and straining until the stone has passed or been surgically removed.

After administering enemas, I x-ray all patients that might have kidney, bladder or urethral stones. Most of these stones are quite visible on x-rays. Occasional the stones contain more organic material than mineral and are difficult to visualize. If I suspect this form of stone, I fill the bladder with air or dye before the x-ray is taken. Ultrasound will also detect these radiolucent stones.

How We Treat Bladder And Kidney Stones:

When bladder or kidney stones are large and unlikely to plug the ureters or the urethra, we may attempt to manage them medically. To do this, we must first have an idea what the stones are made of. Struvite (magnesium ammonium phosphate or triple phosphate) is the most common of all urinary tract stones. Schnauzers and dachshunds seem particularly susceptible to struvite stones. Struvite crystals have a characteristic shape in the urine. Specialty diets are commercially available and can be made at home that encourage stones to dissolve. These diets have reduced protein so less ammonia is formed in the urine. They also contain less magnesium and phosphorus, the building blocks of struvite, as well as more salt to encourage drinking. The more the pet drinks, the more dilute its urine will be and the more likely the stones will dissolve. Since struvite dissolves in acid urine, these diets contain ingredients to keep the urine acidic. A common trade name for such a diet is S/d. A formula for a similar home made diet is given in another article in this series. I generally keep these cases on trimethoprim/sulfa or another urinary antibiotic during this period. I usually give these diets three to five months to work. If the stones have not dissolved completely by then I remove them surgically. Dogs should not be left on this low-protein food for more than five or six months. Cats can stay on their diets longer. Pets that will not eat the commercial diet will often eat the home cooked one.
Urate urinary stone can also sometimes be managed medically. To dissolve these stones we feed diets low in purines with restricted protein. We also administer a drug, allopurinol that reduces the amount of uric acid the body produces.
Certain stones such as calcium oxalate and all those that did not dissolve through medical treatment are removed surgically (cystotomy). Sometimes I choose surgery to end the problem quickly. In female dogs I have been able to reach up into the bladder and crush small stones with a medical instrument called a biopsy punch. This approach requires the use of a fluoroscope. But in most cases, I open the bladder through an incision in its thickest part and manually scoop out the stones. I pass a catheter out the urethra to be sure no stones block it. When a stone is present in the urethra or in the ureter, I move it back into the bladder or kidney and remove it from there. This is so neither the urethra nor the ureters are scared ,constricted and obstruct urine flow. When I am certain all the stones have been removed I flush the bladder with dilute acetic acid and antibiotics and sew it shut like a football. I am very careful that none of my sutures actually protrude on the inner surface of the bladder because they can form the basis for a new stone. To be sure the bladder does not leak, I suture a patch of the veil-like omentum over the bladder incision. To avoid pressure on the bladder incision, I leave a catheter in the bladder for the next two days so that urine does not expand and inflate it.

Stones should be sent to a laboratory for analysis. All stones are less likely to form if your pet has free access to water and frequent opportunities to urinate. Stones are less likely in dilute urine. Adding one quarter teaspoon-full of salt to one pint of water that your pet consumes will increase the amount of water it drinks.

Eliminating bacterial urinary tract infections and checking (bacterial culture and sensitivity) the urine of dogs prone to them twice a year helps prevent stones that occur due to the alkaline urine infections cause.

Diets high in grain and vegetables produce alkaline urine, which allows certain stones to form. This is one of many reasons to see to it that your pet eats a commercially prepared diet.

Calcium Oxalate stones seem to be getting quite common and are very frustrating to treat. They differ from struvite stones in that they form in acidic urine. Unfortunately, they are harder to prevent through dietary manipulation than struvite or urate calculi (stones). Because of this, these stones must be removed surgically and they often reoccur within a few years. They are much more common in male dogs (75%) and Burmese, Himalayan and Persian cats. The most common dog breeds affected are Yorkshire terriers, poodles, shih tzus, schnauzers, lhasa apsos and bichon frises. These stones are associated with excess calcium in the blood and urine. Sometimes these stones are the result of other diseases such as Cushing’s disease or the excessive use of corticosteroid medications. See my article specifically on calcium oxalate.

Many mineral salts are excreted in urine at concentrations at which they would normally fall out of solution and form granules or stones. One substance, produced by the kidneys, called nephrocalcin (an acidic glycoprotein) inhibits stone formation. When too little of this chemical is produced, stones may result.

Some diets recommended for dogs that produce oxalate stones are CNM's (Purina) NF diet, Hills U/D and K/D diets and Waltham's Low Protein Diet. If at all possible feed the canned form of this diet rather than the dry form because dogs rarely drink enough water after eating dry kibble to make up for the water consumed in canned foods. Just be especially sure to brush you dog's teeth when feeding canned diets. Do not feed human table foods in any apreciable quantity.

Life is a trade-off of risks. The drug, furosemide (Lasix) used to treat heart disease in dogs and cats may increase the likelyhood of oxylate stone formation. The same regards corticosteroid drugs such as prednisone and prednisolone and vitamins C and D.

Suplementing your pet's diet with oral potassium citrate (20-37.5mg/pound body weight) given twice a day is thought to lessen the incidence of calcium oxalate stone formation.

If urine specific gravity does not consistently approach 1.015 or less, providing the pet with a thiazide diuretic will increase thirst and produce a diluted urine (hydrochlorothiazide @ 1-2mg/pound body weight twice a day). A blood electrolyte analysis should be conducted several times during the first few months on this medication.

Dalmatians have a propensity for forming urate stones. Male, older dogs are most often affected but I have seen it in litters of Dalmatian puppies. These stones are also found in Yorkshire terriers and English bulldogs.
When stones are composed of more than one type of mineral I try to focus prevention on the mineral that formed the center of the stone.

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8/6/06 Dear Dr. Hines,

Thank you so much for your article on bladder and kidney stones. My puppy, an eight month Standard Schnauzer, had a bladder infection, which did not respond to antibiotics and the infection lead to struvite stones. We did all the traditional treatments and were looking at surgery. I decided to research herbal alternatives and found a natural alternative to antibiotics and surgery - cranberry extract with uva ursi (an herb). There are many references - this link has a short article<http://www.jeanesholistics.com/Cranberryextract.html>I decided to try it - I figured we had very little to loose. Within a
few hours, you could see a visible difference in how the dog was acting - she calmed down, untucked her tail and when she urinated, she had no difficulty. Within 48 hours, her urine was totally clear and had a ph of 6.5.I was amazed at how well this worked. I have personally used cranberry to rid myself of bladder infections, and am so pleased it works for dogs too. After moths of fighting this infection, and seeing my puppy in such discomfort, I wish we had tried this much sooner. Respectfully, Laine

Struvite bladder stones normally form in an acid urine. Perhaps these were struvite stones that precipitate when urine Ph is above 7. . A veterinarian can identify the type by observing the microscopic shape of the crystals. But this is interesting feed-back in any case. Dr. Hines

10/16/06

I am sorry to read about Jackson's oxalate urinary stone problems. The stone that plugged his urethra, actually formed in his bladder. This is a very perplexing disease. We understand so little about it. But I am convinced that the defect that causes these stones to form exists at the DNA code level. As you wrote, the Internet is full of conflicting information.

But one thing is known. Calcium Oxalate crystals will not precipitate out in dilute urine. The problem is, how to get enough water into Jackson to produce a dilute urine. Traditionally, we were taught, that oxalate only comes out of solution when the urine is acid - that is, when urine pH is less than 7. But dilute urine has been found to be the best preventative of stone relapses. The more frequently he urinates the better.

It is next to impossible to keep close track of Jackson's urine specific gravity (diluteness) and pH with periodic samples taken to your veterinarian. PH and specific gravity change hour by hour and pH rises as urine sets in the laboratory awaiting testing. Also, urine pH is usually performed using color indicator strips. This test can be subjective and different staff will interpret pH readings a bit differently. A pH meter is ideal - but few veterinarians have them.

At a human pharmacy, you can purchase a bottle of paper reagent strips that are dipped into fresh urine and then compared to a color chart on the side of the bottle to estimate pH. They are not precises. Some of these have an indicator for specific gravity as well, but it is quite inaccurate. I would prefer that the same member of your family check the urine every day at a specific time and under the same lighting conditions. Time the point of your reading with a watch. I would like you to try to keep Jackson's urine pH between 6.5 and 6.9 - if possible. You must check pH immediately after it is voided because pH rises in urine as a function of time and temperature. Usually, the first void of the morning will have the highest specific gravity.

A simple light microscope with a 10X eye piece and a 10X lens (100X) can detect crystals in urine but one with 10X by 40X lenses is better. Chrystals that I identify as oxalate are crystalline in nature. That is, they have diamond, hexagonal or other sharp lines where the crystal planes meet. Some oxalate crystals that are a series of repetitive plates as well. There are certain rarer metabolic diseases that cause similarly shaped crystals of different composition to form in urine. In most of the normal dogs that I have examined, freshly-collected urine is free of these crystals. However, when the sample is refrigerated, crystals often form in dogs that do not have stone problems. So always examine urine immediately after it is passed. It is perplexing because we know that some dogs that do have suspended oxalate crystals in their urine never develop stones. In a clinical setting, we centrifuge the urine specimen to concentrate the crystals on the bottom.

So I feel that the key to successfully preventing a relapse is to keep a regular check of his urine dilution (specific gravity) and acidity . I would aim for a pH of 6.5-6.8 , that is free of crystals and has a specific gravity of 1.010 - 1.015. Check urine from the first void of the morning. Some dogs with oxalate problems also have kidney problems, and in those dogs the urine is already dilute. Please let me know what his urine specific gravity and blood BUN/Creatinine was. Also, high blood or urine calcium levels can cause the formation of oxalate crystals. If you have that data, send it also.

I would begin him on potassium citrate. Some commercial diets already have it added. Proper amounts of citrate can raise urine pH by about 0.2 points. If his urine pH was actually 5.0 on Hill's u/d diet, then another diet needs to be tried. Whichever brand it is, feed the canned product. You can try CNM's NF diet, made by Nesley-Purina, Waltham's SO or Royal Canine's formula.

As I mentioned, Urine Specific Gravity test strips are very unreliable. The only accurate way to measure Specific Gravity is with a hand held refractometer. Veterinarians, clinical labs producers of
Candy and other food goods use them. They are very simple to operate and inexpensive. There are 237 of them offered on EBay today. Just be sure that it reads in the 1.000 to 1.500 range. It may be described as a "clinical" refractometer. Rinse only the lens area in distilled water between uses and clean the lens with eyeglass tissues. It is easiest to read in bright light. RSS testing for saturation would also be effective but multiple testing is going to be prohibitively expensive. Urine specific gravity will be directly proportional to the amount of water Jackson receives in his diet and water bowl. The more water, the lower the specific gravity the better.

Cysteine , a sulfur-containing amino acid, was found to lower urinary oxalate levels in rats. However, it may have deleterious effects that I am not aware of so I would not use it.

Unfortunately, only about half of the oxalate in Jackson's urine is the result of what he is eating. The other half is being produced by his own metabolism. I know of no way to control that.

Keep several water bowels out for Jackson. Try scenting the water with a flavor he likes. Some dogs enjoy licking from a dripping tap. Prevent dehydration - walk him in the evenings and take water where ever you go.

Dietary recommendations to prevent oxalate stones are a mess. This seems to be due to wide variation in the amount of oxalate found in different samples of the same product. Some thing consistently contain high oxalate levels. Do not feed him chocolate-containing products. Or products containing,soy, peanuts, or sesame, beans, or corn.

Daily examination of Jacksons urine specific gravity and pH are more likely to prevent a relapse than a specialty diet.
You can make your own diet for Jackson if none of the commercial ones are agreeable to him or do not achieve our goals. I am not a nutritionist. If you want a scientifically designed diet, please consult one. Based on what I have read, I might base my diet on white rice, water, ground chicken, cottage cheese or plain yogurt In that order. For the rice, one could substitute items such as canned green peas, caulifflower or cabbage. For the chicken, one can substitute fish which seem to consistently be low in oxalates (haddock, plaice, flounder were examined). Geletin, mustard and salt are also OK. The final diet should contain about 13% protein which is two thirds from meat and one third from dairy and 20% fat on a dry weight basis. A diet with a 13% protein content might not be sufficient for a growing dog. As much distilled water as possible should be included in the mixing. Once this diet is cooled, a portion of a Centrum complete multivitamin should be crushed and mixed in it in proportion to the dog's weight. I would also add some omega 3 and omega 6 fatty acids and possibly some l-carnitine and a small amount of potassium chloride. It is hard to decide how much calcium a diet like this should have. A certain amount of calcium in the diet is required by the body. But high levels of calcium, excreted in the urine encourage oxalate crystal formation. In this diet, dairy products supply the calcium. It is very low in meat. Be particularly cautious of low calcium diets in growing animals. Have your pet's blood calcium level checked periodically. Signs of abnormally low blood calcium level include, weakness, joint pain, convulsions, muscle cramps, abdominal pain, brittle nails, dry scaly skin and periodontal disease. I would have his blood calcium level checked periodically.

Avoid certain medications:
A diuretic called furosemide (lasix) should be avoided as well as cortisone in injectable or pill form, Vitamin C (ascorbic acid) supplements and Sulfa and tetracycline antibiotics. If a diuretec is given to attempt to increase the dog's water consumption, I would use one of the thiazide class as these seem to reduce urine oxalate in humans.

Best wishes, Dr. Hines

At the end of Aug, Jackson our now 16 month old Pug, was diagnosed with calcium oxalate stones adhered to his urethra. Our regular vet took x-rays, flushed his urethra to try to remove as many of the stones as possible, and sent the stones for a lab analysis. The results confirmed that they were calcium oxalate stones. He then had successful surgery to remove them on Sep 5. Approx 2 weeks later, on Sep 20, during our follow-up visit to have his stitches removed, his urine pH registered a 6.5. Then, on or about Sep 25, we started him on a prescription diet -- Hill's u/d.

We have strictly adhered to this prescription diet for the past 3 weeks. Jackson gets no table scraps. For the past 2 weeks, we have been giving him plain cooked chicken as a treat because several websites we've found have listed that as an acceptable treat for dogs with calcium oxalate stones. But, who knows??

However, a follow-up urine test conducted on Oct 13 came back with a 5.0 pH with "a lot of oxalate crystals", as our vet put it. This greatly frustrated my wife and me because Jackson doesn't really like this diet, but even more frustrating is the fact that we got the exact opposite results we were expecting and that this prescription diet was supposed to produce!

There is a ton of information online on calcium oxalate stones, much of it very contradictory. (By the way, I only pay attention to the sites that at least seem to be written and managed by veterinarians or universities; I avoid the personal sites of individual dog owners). For instance, some sites tell you to add salt or chicken broth to the dog's water to induce consumption. Other sites tell you to avoid sodium as much as possible because they can be a cause of these stones. In another example, some of the websites say that diets high in protein PREVENT the stones while others say diets high in protein tend to CAUSE calcium oxalate stones. For a third example of contradictory information, some websites indicate that getting the pH to a more alkaline level ( 6.6+) is the key to preventing these stones. Other sites say that pH is not a reliable test or indicator of whether or not these stones will come back. These sites say that a RSS test is far more reliable.

One final note, we have not yet started Jackson on a potassium citrate supplement.
My basic question is, what the heck are we supposed to do to prevent these stones from coming back?? Jackson is an extremely important part of our family and we want to do anything we can to keep him healthy and happy. But, we don't want to have to put him through surgery 3 or 4 times per year. That just doesn't seem right to us.

Please help. Thank you.

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