Urinary Obstruction in Cats-Causes, Symptoms & Treatment


About       Causes      Symptoms     Diagnosis     Treatment

What is a urinary obstruction?

Medically known as ischuria, a urinary obstruction (UO) is a medical emergency requiring immediate treatment. It occurs when the flow of urine is blocked anywhere along the urinary tract. The most common cause of blockage is a urethral plug which contains mucus, protein, cellular debris, sloughed off epithelial cells and crystals (commonly struvite) in the core. Other causes include:

Urinary crystals

Most commonly struvite and calcium oxalate.

Uroliths (stones)

As crystals grow in size, they can clump together forming uroliths. Struvite forms more commonly in alkaline urine whereas calcium oxalate forms in acidic urine.

Inflammation (urethritis)

Due to crystals, urinary tract infection, trauma, prostate infection or cancer.

Scar tissue

From a previous blockage and catherisation.


Benign or cancerous tumours of the bladder neck or urethra which can cause it to narrow.

Blood clots

These can form in the bladder and cause a blockage as they travel down the urethra which can be related to trauma. I recently read an article about a cat who was found hunched in somebody’s garden. He was taken to a veterinarian who diagnosed a urinary blockage. A catheter was inserted and bloody urine was drained from the bladder along with blood clots. It was later discovered the cat also had a broken pelvis, the trauma had caused blood clots to develop in the bladder.

cat bladder and kidneys

Males are more prone to developing a urinary obstruction than females due to their longer urethra (the tube which drains urine from the bladder through and out of the penis) which narrows inside the penis. However, blockages can develop in females too.

Left untreated, an obstruction can lead to a ruptured bladder and/or a uremic crisis as the kidneys are no longer functioning as they should, toxic levels of nitrogenous waste products (uremia) and potassium (hyperkalemia) build up in the blood and metabolic acidosis develops. It can take as little as 24 hours for this to occur.

A distended bladder can also cause the bladder to lose its tone (bladder atony), resulting in urinary incontinence which may be permanent. Urinary obstruction can occur in cats of all ages, although it is more common in adult male cats.


Urinary blockages can occur slowly, over a period of time, or very suddenly. The exact cause of mucus plug, crystal or urolith formation is not well understood, but contributing factors may include:

  • Diet – This has long been suspected due to the popularity of dry foods over the past 20 years. These diets often change the pH of your cat’s urine, making a more favourable environment for urinary crystals to develop. Dry food only contains a small amount of water compared to a wet diet (raw or canned) which is approximately 70% water. Many cats don’t make up for this imbalance by drinking more, so a cat on dry food will often have very concentrated urine due to inadequate intake. Supersaturated urine is more likely to result in the formation of urinary crystals.
  • Stress – There are two possible reasons why stress can lead to a blockage. Some stressful situations are the result of inter-cat aggression, which can spill over to litter tray usage. The stressed cat may delay going to the toilet for a number of reasons, leading to his urine becoming more concentrated which provides the ideal medium for crystal formation. Chronic stress can also trigger bladder inflammation which can produce large amounts of inflammation and debris.
  • Portosystemic shunt is a congenital disorder in which blood shunts around the liver instead of through. As the liver is responsible for the detoxification of blood, toxins, including ammonia build up which can lead to the formation of ammonium biurate crystals in the urine.


Initially, there may be an incomplete blockage which means your cat is able to urinate but with difficulty. Symptoms of difficult urination may include:

Initially, there may be an incomplete blockage which means your cat is able to urinate but with difficulty.

Early warning signs:

  • Weak flow of urine
  • Frequent trips to the litter tray, but only passing small amounts of urine
  • Painful urination (stranguria)
  • Urinating in inappropriate locations
  • Blood in urine (hematuria)
  • Licking of the genital region

The plug will continue to collect debris until it completely blocks the urethra. Once a complete blockage has occurred, the cat is in danger unless quickly unblocked.

Complete blockage:

A completely blocked cat is in a great deal of pain and discomfort. You may be able to feel the distended bladder towards the rear unless it has ruptured. This is a medical emergency and veterinary attention is vital to unblock your cat.

  • Inability to urinate (many pet owners confuse this with constipation)
  • Sand like material at the tip of the penis
  • Frequent trips to the litter tray
  • Crying when trying to go to the toilet
  • Abdominal pain
  • Abdominal swelling
  • Hiding
  • Licking of the genital region
  • Hunched over appearance
  • Lethargy
  • Pain and/or aggression when touched
  • Loss of appetite

Additional symptoms may occur as the kidneys fail and toxins and potassium build up in the blood. These may include vomiting, loss of appetite, weakness, dehydration, lethargy, abnormal heart rhythm, drunken gait, neurological disturbances, bradycardia (slow heartbeat) and ultimately collapse. Anchor


Your veterinarian should be able to make a tentative diagnosis based on presenting symptoms. He will perform a complete physical examination, at which time he will be able to feel a firm, full bladder, there will also be abdominal pain or discomfort. He will need to run some diagnostic tests to determine the cause and to establish if any damage has occurred to the kidneys. Some tests may include:

  • Blood profiles to check blood potassium, creatinine and nitrogen levels and assess the kidneys for damage, look for signs of infection or systemic disease.
  • Urinalysis to look for infection and crystals in the urine and determine what type they are.
  • X-ray or ultrasound to evaluate for stones, congenital abnormalities, and tumours.
  • ECG (electrocardiogram) to monitor heart rhythm.


Anchor There are several steps involved in unblocking the cat.

  1. Stabilise the cat (treat electrolyte imbalances)
  2. Unobstruct the cat (cystocentesis or catheter)
  3. Supportive care such as pain medication and fluid therapy as well as regular ECG to monitor the heart

Emergency treatment:

  • Lower potassium levels. The first priority is to correct mineral imbalances in your cat. Treating hyperkalemia with calcium gluconate to which antagonises the effect of hyperkalemia on the heart. Insulin/dextrose can help to shift potassium into the cells and sodium bicarbonate raises blood pH which also drives potassium into the cells.
  • Catheterisation to relieve obstruction which allows the bladder to void urine and may be in place for several days afterwards. Heavy sedation is necessary to catheterise the cat, which involves the insertion of a thin tube into the penis and up to the bladder. A sterile solution is flushed through the tube to push the obstruction back into the bladder, where it will dissolve or be surgically removed.

Medical management:

Once the obstruction has been removed, the kidneys are able to resume their job of urine production, removing toxins from the bloodstream. In the days after, urine production is increased (post-obstructive diuresis) as the kidneys cleanse the blood. Intravenous fluids will be continued to prevent dehydration and electrolyte derangements such as hypokalemia (low blood potassium) due to increased urine output.

  • During this time, the catheter will remain in place, and the veterinarian will monitor urine output.
  • Painkillers to relieve discomfort.
  • Antispasmodic medications such as Prazocin to relax the urethra.
  • Antibiotics, if indicated.

Addressing the underlying cause will be necessary to prevent future occurrences. Increase water consumption to dilute the urine and feed a canned or raw diet as this contains a higher amount of water than dry food.

  • Dissolving crystals:  If your cat has urinary crystals, your veterinarian can prescribe a prescription diet such as Hills c/d or s/d to dissolve them and maintain urine pH.
  • Surgery to remove stones (cystomy): Uroliths which are too large to be dissolved or flushed out will need surgical removal.

Once the stones have been removed, they will be sent off to determine the type and a culture will be performed to determine what (if any) bacteria are also present so the most suitable antibiotic can be prescribed.

  • Perineal urethrostomy: This surgery is necessary for cats who have repeat blockages. It involves surgery to create a new urethral opening.


Follow your veterinarian’s instructions and administer medication as prescribed. Keep a close eye on your cat’s litter tray usage and take him straight to the veterinarian if he shows signs of blockage.

Increasing water consumption is important to keep the urine as dilute as possible which decreases the chances of crystal formation.

Switch to a wet diet and encourage your cat to drink by adding more water bowls or introducing a water fountain bowl, which many cats love.

Keep the cat as stress-free as possible to reduce the chances of a recurrence.

Keep litter trays scrupulously clean, remove solids twice a day and completely empty once a week. Provide several trays for multi-cat households. The general rule of thumb is one tray per cat, plus one extra.