FELINE OXALATE BLADDER STONES
The cat with bladder stones tends to have the classical symptoms of feline idiopathic cystitis: straining to urinate, bloody urine, urinating in unusual places, genital licking. In the course of testing to pursue these symptoms, a radiograph is taken and a stone or group of stones is seen in the urinary bladder. Alternatively, the cat might have no symptoms of any kind and the stone is discovered when a bladder infection fails to resolve after appropriate antibiotics. The stone may be found incidentally when the cat has radiographs taken for some other reason. At the point where we see the stone on the radiograph or on an ultrasound image, we do not know what kind of stones we are up against. To find out we must:
Unlike Struvite stones, Calcium Oxalate stones cannot be dissolved with special diets; surgery is needed to remove any stones too large to pass.
WHY DO CATS DEVELOP CALCIUM OXALATE BLADDER STONES?
In older times (25 years or so ago), cats virtually never developed calcium oxalate bladder stones. Cat bladder stones could reliably be assumed to be made of struvite (a matrix of ammonium-magnesium-phosphate). In those days, feline lower urinary tract symptoms were generally thought to be caused by struvite crystals in urine and feline lower urinary tract symptoms were extremely common. The pet food industry responded by acidifying cat foods to prevent the development of crystals. In a way it worked. Feline lower urinary tract symptoms declined. Male cats with struvite urinary blockages became far less common. The trade off was that calcium oxalate bladder stones began to develop. Acidifying the body leads to an acid urine pH and more calcium loss into the urine, both factors in the development of a calcium oxalate stone. Currently most bladder stones formed by cats are calcium oxalate stones.
35% of cats with calcium oxalate bladder stones
Cats with calcium oxalate bladder stones tend not to have crystals in their urine
Cats with calcium oxalate stones tend not to have bladder infections
HOW TO GET RID OF THE STONES
CYSTOTOMY (SURGICAL REMOVAL)
USING DIET TO DISSOLVE A CALCIUM OXALATE STONE IS NOT POSSIBLE.
ONCE A STONE HAS BEEN RETRIEVED,
Retrieving the stones is generally the easy part of calcium oxalate stone management. Prevention of future stones is more challenging. If the patient is one of the 35% with an elevated blood calcium then steps to control the calcium level and determine why it is high should be taken. (See Hypercalcemia). If blood calcium levels are normal, the following step by step regimen is recommended:
STEP ONE: FEED A NON-ACIDIFYING DIET THAT MINIMIZES CALCIUM OXALATES IN URINE
Such diets use a normal calcium content, a moderate magnesium content, and citrate to bind urinary calcium. Hills c/d multicare diet, Royal Canin S/O, Iams Eukanuba Moderate pH/O, and Purina UR st/ox are all appropriate foods. Canned diet is preferred over dry food due to the high water content of canned foods. Part of the goal is to create a dilute urine and the extra water consumption is helpful. Meal feeding rather than free feeding also may be helpful in maintaining the desired urinary pH.
Avoid supplementation with vitamin C. Vitamin C is converted to Oxalic acid which modifies into oxalate. Be careful of pet vitamin supplements.
In 2-4 weeks, a urinalysis is performed to see if there are calcium oxalate crystals present (there should not be), if the urine is dilute (the specific gravity of the urine should be less than 1.020), and if the urine pH is alkaline (it should be 6.8-7.5).
Oxalate crystals are classically marked with an “X” (the “X” is naturally present in the crystals when viewed under a microscope)
STEP TWO: CORRECTING PROBLEMS IN THE FIRST URINALYSIS
If the urine specific gravity is > 1.020, this means that the urine is not adequately diluted. The cat will need to drink more water. This is best accomplished by increasing the percentage of canned food in the diet.
If the urinary pH is <6.5, the urine is too acidic and potassium citrate must be given as a supplement, either as a chewable tablet, capsule or oral liquid.
Another urinalysis is performed in 2-4 weeks.
STEP THREE: IF OXALATE CRYSTALS ARE PRESENT, THE URINE IS NOT DILUTE, OR IF THE PH OF THE URINE IS ACID (pH < 7.5) THE FOLLOWING STEPS ARE TAKEN:
A thiazide diuretic is added to dilute the urine and correct the necessary electrolyte balance in the urine. Vitamin B6 is supplemented. A population of cats has been identified for which a B-6 deficiency leads to oxalate stone development. This may or may not be helpful but is worth trying. The vitamin B-6 deficiency leads to an increase in blood oxalic acid which in turn leads to an increase in urine oxalates. A different food may need to be selected
Once a urinalysis with the appropriate values is obtained, the patient is rechecked every 3-6 months with both a urinalysis and radiographs. If the patient is female, stones may be identified when they are still small enough to be induced to pass naturally. A male cat will require surgery to remove stones as the male tract is invariably too small for the passage of stones.
Page last updated: 9/6/2012