CONDITION
Ureteral Obstruction in Cats
Ureteral obstruction occurs when one or both of the narrow tubes that carry urine from the kidneys to the bladder become blocked. In cats, this is most often caused by small stones that form in the kidney and become lodged as they travel down the ureter, though scar tissue, blood clots, or less commonly tumours can also create a blockage. The obstruction prevents urine from draining normally, and pressure can build back up into the affected kidney. Owners often notice reduced appetite, quiet behaviour, or vomiting that may seem vague at first. Some cats show discomfort in the abdomen or back, though this is not always obvious. The condition tends to develop over hours to days, and the signs can be subtle until the obstruction has been present for some time. It is more common in middle-aged to older cats, and some individuals form stones more readily than others. This page explores the patterns that may prompt investigation, what is happening inside the urinary tract when flow is interrupted, the imaging and tests used to identify and locate an obstruction, and the range of approaches—from medical management to surgical or minimally invasive procedures—that exist depending on the nature and duration of the blockage.
Why this matters now
Ureteral obstruction is seen most often in middle-aged to older cats, typically between five and fifteen years of age, though younger animals can also be affected. Cats with a history of urinary stone formation are at higher risk, and certain metabolic tendencies—such as high calcium excretion or concentrated urine—can increase the likelihood of stone development. Some breeds, including British Shorthairs and Ragdolls, may form stones more readily, though the condition can occur in any cat. Diet, water intake, and underlying kidney function all contribute to the pattern of stone formation over time.
The obstruction may develop suddenly when a stone moves from the kidney into the ureter, or it may build more gradually as scar tissue narrows the passage. In the first hours to days, the affected kidney continues to produce urine that cannot drain, and pressure rises within the collecting system. Some cats show subtle signs early on, while others remain quiet until the obstruction has been present long enough to affect kidney function or cause secondary changes such as infection or inflammation. The timeline and severity vary considerably between individuals, and partial obstructions may allow intermittent drainage, which can make the pattern less obvious.
Signals & patterns
Early signals
Reduced appetite or quiet eating
A cat may begin to eat smaller portions or show less interest in meals over a day or two. This can reflect mild nausea or generalised discomfort, and it often appears before other signs become clear.
Vomiting, often infrequent
Occasional vomiting may occur, sometimes containing food or clear liquid. It tends to be sporadic rather than persistent, and it can be mistaken for hairballs or a dietary upset.
Quieter behaviour or withdrawn demeanour
Some cats become less interactive, spending more time resting or hiding. This is a non-specific sign, but it can reflect the body's response to rising pressure in the urinary tract or early changes in kidney function.
Subtle abdominal or flank discomfort
A cat may shift position frequently, be reluctant to be picked up, or show mild tension when the abdomen or back is touched. This is not always obvious, and many cats do not vocalise when uncomfortable.
No change in litter tray use
Unlike lower urinary tract conditions, ureteral obstruction does not typically cause straining or frequent trips to the litter tray. Urine output may remain normal or even increase if only one ureter is affected, which can make the condition harder to recognise early on.
Later signals
Persistent vomiting or reduced water intake
As kidney function declines, waste products accumulate in the bloodstream, and nausea can become more pronounced. A cat may stop drinking or vomit more frequently, which further contributes to dehydration.
Marked lethargy or unresponsiveness
A cat may become noticeably less alert, reluctant to move, or slow to respond to interaction. This reflects more advanced changes in blood chemistry and the body's inability to clear toxins effectively.
Weight loss or muscle wasting
Over days to weeks, a cat may lose condition as appetite remains poor and the body begins to break down its own tissues. This is more common when obstruction is prolonged or when both ureters are affected.
Visible abdominal discomfort or arched posture
Some cats adopt a tense, hunched posture or show clear discomfort when the abdomen is approached. This can indicate more significant distension of the kidney or secondary inflammation in the surrounding tissues.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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