At a glance
About: Urolithiasis is the formation of stony concretions on the bladder or urinary tract. Factors which lead to uroliths include the oversaturation of urine which can be exacerbated by feeding a dry diet.
- Pain when urinating
- Inability to urinate
- Blood in the urine
- Crying in the litter tray
Stone dissolving diets, catheterisation, surgical removal of stones, and increase water consumption.
Uroliths are rock-like stones within the urinary tract that cause irritation and secondary infection. Struvite (also referred to as magnesium ammonium phosphate or MAP) account for approximately 65% of stones, 20% are calcium oxalate , other stones include calcium phosphate, ammonium urate, silica, and cystine. It is essential that the veterinarian identifies which stone(s) your cat has and treats accordingly.
Image courtesy Southern Cross Veterinary Clinic
Crystals develop and combine to form stones over time. They are composed of a small amount of organic matrix, which is made up of mucoprotein, surrounded by layers of polycrystalline (many crystals) concretions.
Urinary stones can lead to inflammation of the urinary tract, which may lead to urinary tract infection , or they can cause a urethral blockage, especially in male cats, leading to urinary obstruction. Blockage leads to uremic poisoning and hyperkalemia (high blood potassium), which is life-threatening.
The underlying feature of urolithiasis is pain and difficulty passing urine.
- Frequent urination (pollakiuria), only passing small amounts of urine.
- Hematuria (blood in urine).
- Sudden halt in litter box usage or urinating outside the litter tray.
- Dysuria (painful and difficult urination). You may hear your cat crying near, around or in the litter box. The cat attempts to urinate but only passes a small amount of urine.
- Straining to urinate, only letting out a few drops (if any) at a time which many pet owners mistake for constipation.
- Excessive genital licking, way beyond regular self-cleaning.
- Urinating in places other than the litter box, such as the bath or floor.
Your veterinarian will perform a complete physical examination and obtain a medical history from you. This examination will include abdominal palpitation, including the bladder. Most uroliths in the bladder are not palpable. However, your veterinarian may discover a full bladder as a result of obstruction.
- Urinalysis: To check for the presence of blood (hematuria), white blood cells (pyuria, bacteria (bacteriuria) and crystals (crystalluria) in the urine, which will also show the pH of the urine.
- X-ray or ultrasound: This will show the location and size of the uroliths.
- Intravenous pyelogram (IVP/excretory urography): To see very small or radiolucent (transparent to x-ray) uroliths may require contrast radiography. The veterinarian injects a contrast medium (dye) is injected into a vein, and it is excreted via the kidneys where it appears in the urine and enables the technician to view the structures of the urinary tract.
- Microscopic analysis of the stones: To determine what type of stone(s) your cat has which will help the veterinarian determine the treatment plan.
Treatment depends on the cause and severity of the condition as well as the type of crystals involved.
As stone build-up is caused by supersaturation of urine, it is essential to increase water consumption, which dilutes the urine. It is also beneficial to aim for a pH below 6.5. pH in a cat’s urine usually ranges from 5.5 to 8.0, but diets which result in < 6.5 decreases the chances of struvite crystals forming.
- Diet: Moisten dry food or change to canned/raw food to increase water consumption. Dry food contains approximately 10% water, whereas canned or raw food contains 70% water, and most cats don’t compensate by drinking more water. Avoid fish flavoured food. Feed a diet which increases the acidity of urine.
- Stone dissolving diets: These diets are low in magnesium and acidifying; however, they are only effective for struvite stones. Unfortunately, long-term use of an acidifying does carry some risks, one of which is the increased chances of developing calcium oxalate urolithiasis. It can take several months to dissolve stones.
- Increase water consumption: Encourage drinking by other means, such as providing a drinking fountain for your cat.
- Antibiotics: To treat urinary tract infections.
Catheterisation: The veterinarian places a catheter into the urethra to flush out small uroliths.
Therapeutic cystocentesis: A routine veterinary procedure with the use of a needle and is inserted through the abdominal wall to remove urine directly from the bladder. This is typically a last resort, and a catheter is a preferred method in the blocked cat.
Surgical removal of uroliths: The advantage of surgical removal is that the stones are completely removed and can be identified. However, as with any surgery, there are also risks.
Voiding urohydropropulsion: Flush the bladder with a sterile liquid to void it of stones.
Retrograde urohydropropulsion: Flush stones in the urethra back into the bladder.