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
Investigation typically begins with a review of the cat's recent behaviour, appetite, and urination pattern, followed by a physical examination to assess comfort, hydration, and the size and texture of the kidneys through the abdominal wall. When ureteral obstruction is suspected, imaging becomes the central tool for confirming the blockage and locating it, while blood and urine tests help clarify how kidney function has been affected. The combination of these approaches builds a picture of whether one or both ureters are involved, what material is causing the obstruction, and how urgently intervention may be needed.
Blood biochemistry
Urinalysis
Abdominal ultrasound
Radiography
Contrast imaging or CT
Options & trade-offs
Management is shaped by the location and nature of the obstruction, how long it has been present, whether one or both kidneys are affected, and the cat's tolerance for different procedures. Some obstructions resolve with medical support and time, while others require direct intervention to restore flow. The approaches are often combined, and what works well for one cat may be less suitable for another depending on temperament, concurrent health problems, and the practicalities of home care.
Medical management and observation
This involves intravenous fluid therapy to support kidney function and maintain hydration, alongside monitoring of blood values and urine output over several days. The aim is to reduce the size of a stone, encourage it to pass spontaneously, or allow inflammation and spasm in the ureter to settle. Pain relief and medications to relax the ureteral wall are often used during this period.
Trade-offs: This approach can be effective for partial obstructions or small stones, but it requires close monitoring and repeated blood tests, and there is no guarantee the stone will pass. If the obstruction persists, kidney function may continue to decline, and more invasive intervention may become necessary after a period of waiting.
Subcutaneous ureteral bypass
A small device is surgically implanted to route urine from the kidney directly to the bladder, bypassing the obstructed ureter. A tube with ports at each end is placed under the skin, connecting the renal pelvis to the bladder, and urine flows through the device rather than the natural ureter. This is typically performed under general anaesthesia by a specialist surgeon.
Trade-offs: The procedure restores urine flow reliably and can be used even when the ureter is severely damaged or scarred. However, it requires surgery, carries risks of infection or device blockage over time, and necessitates lifelong monitoring of kidney function and the device itself. Some cats tolerate the implant well for years, while others may develop complications that require revision or removal.
Ureteral stenting
A narrow tube is threaded through the ureter to hold it open, allowing urine to flow past the obstruction. The stent is placed during a minimally invasive procedure under anaesthesia, often guided by imaging, and remains in place permanently. The stent spans the length of the ureter from the kidney to the bladder.
Trade-offs: Stenting avoids the need for a bypass device and can resolve the obstruction without extensive surgery. However, stents can migrate, become blocked by mineral deposits, or cause irritation and inflammation in the ureteral wall. Long-term outcomes vary, and some cats may require stent replacement or additional intervention if complications arise.
Surgical ureteral exploration and stone removal
An incision is made into the ureter to remove a stone or other obstructing material directly. The ureter is then repaired with fine sutures, and the abdomen is closed. This approach is sometimes combined with placement of a temporary stent to support healing.
Trade-offs: Surgery allows direct removal of the obstruction and can be effective when the stone is lodged in a specific, accessible location. The ureter is delicate and can be difficult to suture without causing further narrowing or scarring, and healing may be complicated by leakage of urine or stricture formation. Recovery involves careful post-operative monitoring and pain management.
Dietary and environmental modification
Adjusting the type of food, increasing water intake, and managing factors that influence urine concentration and pH can reduce the formation of new stones and may help existing small stones to dissolve or pass. This approach is often used alongside other interventions and continued long-term to lower the risk of recurrence.
Trade-offs: Dietary changes are non-invasive and can be sustained at home, but their effectiveness depends on the composition of the stones and the cat's willingness to accept the new diet. This approach does not resolve an acute obstruction and is better suited to prevention or support after flow has been restored by other means.
Common misconceptions
"Ureteral obstruction and urethral obstruction are the same condition."
The ureters carry urine from the kidneys to the bladder, while the urethra carries it from the bladder to the outside of the body. Urethral obstruction is more common in male cats and typically involves the bladder and lower urinary tract, whereas ureteral obstruction affects the passage between the kidney and bladder and can occur in either sex. The signs, investigation, and management of the two conditions differ considerably.
"If a cat is still urinating, the ureters cannot be obstructed."
Cats with obstruction of one ureter can continue to produce and pass urine from the unaffected kidney, so normal or near-normal urination does not rule out the condition. Even partial obstruction of both ureters may allow some urine to reach the bladder intermittently. The volume and frequency of urination may change, but the pattern can be subtle and is not always a reliable guide to whether flow is blocked higher up in the urinary tract.
"Once an obstruction is treated, the problem is resolved and will not return."
Cats that have formed one stone often have an underlying tendency to form more, and without long-term dietary or environmental management, recurrence is common. Scar tissue from the initial obstruction or surgical repair can also create new narrowing over time. Ongoing monitoring of kidney function, urine composition, and imaging at intervals is often part of managing the condition in the months and years after treatment.
Related conditions
Ureteroliths
Ureteroliths are stones lodged within the ureter itself, and they represent the most common cause of ureteral obstruction in cats. The two conditions describe overlapping clinical pictures—one naming the blockage by location, the other by the object creating it.
Urinary Stones (Urolithiasis)
Urinary stones that form in the bladder or kidneys can migrate into the ureter and cause obstruction as they travel. Understanding stone composition and the factors that promote their formation is often relevant when investigating ureteral blockage.
Hydronephrosis
Hydronephrosis describes the swelling of the kidney that occurs when urine cannot drain normally, and ureteral obstruction is one of the most common causes of this back-pressure and stretching of the kidney's collecting system.
Acute Kidney Injury
Ureteral obstruction can lead to acute kidney injury if the blockage is complete and sustained, particularly when both ureters are affected or when the cat has only one functioning kidney. The sudden loss of drainage creates conditions in which kidney tissue may be damaged over hours to days.
Pyelonephritis
Obstruction of the ureter can create an environment in which bacteria may ascend more readily toward the kidney, and in some cases infection and obstruction may occur together or one may predispose to the other.
The broader context of kidney health and urinary stone formation may be relevant, particularly if the cat has a history of urinary crystals, changes in thirst or urination, or chronic kidney disease. Understanding the metabolic tendencies that contribute to stone development can inform longer-term decisions about diet and monitoring. If surgical or interventional procedures have been discussed, it can be useful to explore what different approaches involve and how they might fit with the cat's temperament and home environment over time.