Feline Urolithiasis – Calcium Oxalate Stones
Calcium oxalate uroliths, also referred to as calculi, are stones within the urinary tract composed of the mineral calcium oxalate. Clinical symptoms depend on the size and number or uroliths as well as their location in the urinary tract. Some affected animals may have no clinical signs. Calcium oxalate stones affect cats of all ages, but are most common in middle-aged pets, and the Persian is the feline breed most commonly affected.
Causes of Calcium Oxalate Stones in Cats
In most cases, the cause of calcium oxalate stone formation remains unknown despite thorough medical evaluation of the pet. However, several conditions may contribute to the formation of calcium oxalate calculi. These include:
Excessive dietary calcium, protein, and sodium, which may promote excessive excretion of calcium in the urine
Any disease that causes high levels of calcium in the blood
Administration of large amounts of cortisone-like drugs (corticosteroids) or some diuretics (furosemide), which may also promote excessive excretion of calcium in the urine
Inadequate amounts of inhibitors of crystal growth or defective inhibitors, which are natural substances present in the urine that inhibit the growth of calcium oxalate crystals
Excessive excretion of oxalate in the urine
What to Watch For
Passage of small amounts of urine
Increased frequency of urination
Inability to urinate
Diagnosis of Calcium Oxalate Stones in Cats
Routine diagnostic tests include a complete blood count (CBC), biochemical profile and urinalysis. Although these test results often are normal, changes consistent with kidney failure or bacterial urinary tract infection may be observed. If increased blood calcium concentration is observed, the pet should be evaluated for causes of hypercalcemia, especially primary hyperparathyroidism (overproduction of parathyroid hormone by a benign tumor in the parathyroid gland).
Calcium oxalate crystals may be present in the urine, but not in all cases. The absence of calcium oxalate crystals in the urine does not rule out the presence of calcium oxalate calculi. Finally, calcium oxalate crystals can be observed in the urine of normal cats as well as in the urine of cats with other medical problems (antifreeze poisoning).
Bacterial culture of the urine should be obtained to rule out bacterial urinary tract infection.
Abdominal radiographs (X-rays) or ultrasound can be used to identify calcium oxalate uroliths in the urinary tract. Calcium oxalate stones are radio dense due to the presence of calcium and can be recognized as white objects within the bladder or other parts of the urinary tract on plain abdominal radiographs.
Treatment of Calcium Oxalate Stones in Cats
There are no successful treatment protocols that can dissolve calcium oxalate stones. Your veterinarian will probably recommend any of the following:
Urohydropulsion (flushing stones out of the bladder with sterile saline) and catheter retrieval are techniques that can be used to remove small stones (less than 5 mm in diameter) from the lower urinary tract (urethra and bladder). If urohydropulsion is ineffective, other treatment options must be considered.
Surgical removal of calcium oxalate stones is recommended for patients with urinary tract obstruction or severe pain on urination arising from stones that cannot be relieved manually.
Lithotripsy is a technique that uses shock waves to break up stones and may be performed at some specialized referral centers. This procedure requires general anesthesia and special expertise and equipment to perform.
Fluid therapy may be indicated if there is associated kidney disease, urinary obstruction or dehydration.
Antibiotic therapy is indicated in those patients with concurrent urinary tract infections.
Administer any medications and feed special diet as prescribed by your veterinarian. Watch for the recurrence of clinical symptoms because calcium oxalate stones tend to recur.
Potassium citrate may be of benefit because it increases urine pH (it makes the urine more alkaline) and inhibits calcium oxalate stone formation.