A cat that keeps going to the litter box, strains and passes little or no urine may have a blocked urethra, and that is an emergency: go to a vet or an emergency clinic now, at any hour. Cornell's Feline Health Center says the time from a complete blockage to death may be less than 24 to 48 hours. It happens almost only in male cats, and the straining is easy to mistake for constipation.
The urethra is the tube that carries urine from the bladder out of the body. In a blocked cat something is stuck in it. The Merck Veterinary Manual says the most common cause is a plug of protein, cell waste and mineral crystals, and that stones, tumors and blood clots can block it too. Cornell says male cats are at greater risk than females because their urethra is longer and narrower, and International Cat Care's 2025 guidelines say a blockage occurs almost only in males.
When urine cannot leave, Cornell says, the kidneys become less able to remove toxins from the blood and to keep the body's fluids and salts in balance. The Merck manual says the abnormal salt levels can cause life-threatening changes in the heart's rhythm. The American College of Veterinary Surgeons (ACVS) says most affected cats are between 1 and 10 years old.
Cornell lists the signs of trouble in the bladder or the urethra:
A blocked cat starts the same way, Cornell says: it strains, tries again and again, and produces little or no urine. As time passes it becomes much more distressed and often cries out in pain. The ACVS adds restlessness, hiding, loss of appetite and lethargy, and the Merck manual adds vomiting.
Both the Merck manual and the 2025 guidelines warn that owners can mistake these signs for constipation. If you cannot tell whether urine is coming, treat it as a blockage. The same signs with urine still passing can come from bladder inflammation, stones or an infection. They need a vet visit too, and the Merck manual says a male cat with bladder inflammation may go on to block.
| Test | What it looks at | What it tells the vet |
|---|---|---|
| Feeling the belly | The size and feel of the bladder. | The Merck manual says a blocked animal typically has a hard, swollen and painful bladder. |
| Blood test | Potassium and other salts, and the waste products the kidneys clear. | How far the blockage has upset the body. The Merck manual says very high potassium can cause life-threatening heart rhythms. |
| Heart tracing, ECG | The rhythm of the heart. | Whether the potassium is affecting the heart. |
| Urine test | Crystals, and bacteria if the urine is cultured. | The ACVS says the urine is checked for crystals and may be sent for a culture, which shows whether there is an infection. |
| X-rays | Stones in the kidneys, the bladder or the urethra. | Whether a stone is the cause. The Merck manual says x-rays should always be part of the workup. |
| Ultrasound | The inside of the bladder. | The 2025 guidelines use it to find stones, growths and blood clots. |
Petipedia explains each kind of test: the blood test, the urine sample, and x-rays and ultrasound.
The 2025 guidelines put the cat's condition first: fluids into a vein, pain relief as a priority, and treatment of the high potassium. Then the blockage is cleared. The ACVS says the cat is sedated or anesthetized so that a catheter, a thin tube, can be passed into the urethra to flush out the plug or push a stone back into the bladder. The catheter typically stays in for a few days until the swelling goes down.
Cornell says hospital stays range from a few days to several weeks. In the study described below, half the cats kept in hospital stayed 3.5 days or less.
Cornell says a struvite stone may be dissolved with a special diet, while a calcium oxalate stone cannot and often needs more aggressive treatment. Antibiotics are for an infection, and infections are uncommon here: Cornell says bacteria cause only one to three percent of lower urinary tract disease in young to middle-aged cats, and around 10 percent in cats older than 10. Ask whether a urine culture was done before you pay for antibiotics.
For a cat that keeps blocking despite proper medical care, Cornell and the ACVS describe an operation called perineal urethrostomy, which removes the narrow part of the urethra and leaves a wider opening. The ACVS says it does not prevent bladder inflammation or stones, and that bacterial urinary infections occur in 25% of cats within the first year after it. Neither source describes it as the first step after a single blockage.
Most treated cats survive. A study in the Journal of Feline Medicine and Surgery covered 82 blocked male cats treated at the Hebrew University's teaching hospital from 2006 to 2008. Of the 71 cats with a known outcome, 6 (8.5%) did not survive. Of the 50 cats followed afterwards, 22% blocked again within six months and 24% within two years.
Bladder inflammation without a blockage tends to return as well. The Merck manual says its signs usually pass in 2 to 7 days and that about half of affected cats have another episode within a year. Cornell's long view is more hopeful: most cats rarely have the problem again or have only occasional recurrences.
Cornell's steps for lowering the risk are clean, fresh water, small meals often, a healthy weight, one more litter box than the number of cats, clean boxes in quiet places, and as few big changes in routine as possible. The 2025 guidelines add that wet food and more water may help prevent another episode.
None of these sources gives a price, so there is none here. The bill covers an emergency visit, sedation or an anesthetic, tests and usually some days in hospital. Ask for a written estimate at the start, and say so if money is tight. See what a vet bill costs, what to do when you cannot pay it and what happens at the emergency vet.
Now, whenever a cat strains and you see little or no urine.
The sources give different times. Cornell says death may come less than 24 to 48 hours after a complete blockage, the Merck manual's page for owners says a cat may die within 2 to 3 days without treatment, and the ACVS says 3 to 6 days. None of them describes a safe wait. The 2025 guidelines say waste products build up in the blood within 24 to 48 hours.
Call the clinic to say you are coming, and do not wait for morning. The other emergency signs are on Cats: is this an emergency?
If something here is out of date, tell us at hello@petipedia.io and we fix it the same day.
Sources read on 2 October 2026; every number is as the source gives it. One of the Cornell pages carries no date, and the 2011 study covers one hospital.