Also known as uroliths or calculi, bladder stones are rock-like deposits in the urinary bladder. The cause of bladder stones is concentrations of certain minerals in the urine. The most common types are struvite and calcium oxalate. Other less common bladder stones include ammonium urate, calcium-ammonium-phosphate, urate, cystine and compound (stones which contain different materials).
Bladder stones get their name after their mineral formation. It is important that your veterinarian identifies which stone(s) your cat has and treats accordingly. They form due to the presence of excess quantities of certain minerals in the urine, other contributing factors include persistently infected bladder, genetic predisposition, dietary, portosystemic shunt and urine pH.
Bladder stones run the risk of causing a potentially fatal urinary obstruction which is a medical emergency that requires immediate veterinary attention. Symptoms of a urinary obstruction include straining to urinate, frequently visiting the litter tray, urinating in inappropriate spots, genital licking, and crying. Males are at greater risk of a urinary obstruction due to their narrower urethra.
Struvite stones come in two categories, infected and sterile. Infected struvite stones are the result of bacteria which produce an enzyme that raises the urine pH, increasing the amount of ammonium and phosphate in the urine. Sterile struvite stones are associated with specific diets that contain high levels of magnesium.
Calcium oxalate stones are again they are the result of acidic urine and in the past, struvite stones were by far the most common type of bladder stone to affect cats, however, calcium oxalate stones are now gaining ground.
Frequent urination which often produces only a few drops
Your veterinarian will perform a complete physical examination and obtain a medical history from you. The examination will include abdominal palpitation, including the bladder, as stones in the bladder are not palpable, your veterinarian may discover a full bladder as a result of obstruction.
Your veterinarian will wish to perform some tests, some of which may include;
Urinalysis – To check for the presence of blood (hematuria), white blood cells (pyuria), bacteria (bacteriuria) and crystals (crystalluria) in the urine, this will also show the pH of the urine.
X-Ray or ultrasound – To identify most stones, this will also show the location and size of the stones.
Intravenous Pyelogram (IVP/excretory urography) – To see very small or radiolucent (transparent to x-ray) stones which may require contrast radiography. A contrast medium (dye) is injected into a vein which the kidneys excrete via the urine. This enables the technician to view the structures of the urinary tract.
Analysis of the stones – To determine what type of stone(s) your cat has, this will help your veterinarian determine the treatment plan. It is only possible to determine the type of bladder stones by surgical removal, or in some cases, if one is passed in the urine.
What is the treatment of bladder stones in cats?
Treatment will depend on the type of stone and may include:
Antibiotics – To treat a bladder infection, if one is present.
Prescription diet – These alkalizing diets assist in dissolving the stones and alter the pH of the urine. It can take several weeks to several months for stones to dissolve. Diets are not always completely successful and not all types of stone can be dissolved by diet.
Urinary acidifiers – These tablets can be used in conjunction with diet to assist with lowering the pH of the urine.
Increase water consumption- This may include switching the cat to a moist diet which has a higher water content and encouraging your cat to drink more water.
Surgical removal of the stones is 100% successful and has the advantage of confirming the type of stone involved. There are risks with any form of surgery, and there is a recovery time, however, surgery is the only option if a diet fails to dissolve the stones or if they are the type of stones that diet alone can’t treat.
Your veterinarian will wish to follow up with you after several weeks with additional x-rays to see if the stones are dissolving (in the case of diet), or have returned.