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 type is struvite, which accounts for 50% of stones, other types include calcium oxalate, 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 crucial that the veterinarian identifies which stone(s) your cat has and treats accordingly. Bladder stones form due to supersaturation of urine. Other contributing factors include a 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 urinary obstruction include straining to urinate, frequently visiting the litter tray, urinating in inappropriate spots, genital licking, and crying. Males are at higher risk of 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 high magnesium diets.
Calcium oxalate stones are the result of acidic urine. In the past, struvite stones were by far the most common type of bladder stone; however, calcium oxalate stones are now gaining ground.
- Frequent urination which often produces only a few drops
- Difficulty urinating (dysuria)
- Crying in the litter tray
- Blood in the urine (hematuria)
- Urinating outside the litter box
- Genital licking
Your veterinarian will perform a complete physical examination and obtain a medical history from you. The exam 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 urine pH.
- Urine sediment exam: Microscopic examination of sediment from a urine sample which can help to determine the type of stones.
- 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 which enables the technician to view the structures of the urinary tract.
- Analysis of the stones: Definitive diagnosis of the type of stone will require laboratory analysis of a stone sample.
- Stone dissolving diets: These alkalising 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 entirely successful, and it is not possible to dissolve all types of bladder stone with diet.
- Antibiotics: To treat a bladder infection, if one is present.
- Urinary acidifiers: These tablets can be used in conjunction with a diet to lower the pH of urine.
- Increase water consumption: Switch the cat to a moist diet which has a higher water content. Encourage water consumption with multiple water stations and/or water fountains.
- Surgical removal of the stones that cannot be dissolved by diet. Advantages are that it is 100% successful and will confirm the type of stone involved. The veterinarian makes an incision in the bladder and removes the stones with forceps.
Always follow discharge instructions which the veterinarian will provide when the cat goes home.
Monitor the cat for signs of urinary blockage and seek immediate veterinary attention if symptoms return.
A follow-up will be scheduled at which time x-rays will be performed to see if the stones are dissolving (in the case of diet), or have returned.