CONDITION
Urethral Obstruction
Urethral obstruction occurs when the tube that carries urine from the bladder to the outside (the urethra) becomes blocked, preventing a cat or dog from emptying their bladder normally. The blockage can be partial or complete, and may develop over hours or days. Male cats are particularly prone, though it can occur in any cat or dog. Owners often notice repeated trips to the litter tray or garden with little or no urine produced, straining that may resemble constipation, or vocalisation during attempts. Some animals may lick at the area persistently or seem restless and uncomfortable. The early signs look much like those of cystitis or constipation, and whether the bladder is emptying cannot be judged at home. A complete blockage is life-threatening, with death reported in less than 24 to 48 hours. This page explores the patterns that may prompt concern, what can cause or contribute to a blockage, how the condition is confirmed and monitored, and the range of approaches used to relieve the obstruction and support recovery. The focus is on helping owners recognise what they may be observing and understand the shape of the problem.
Why this matters now
Urethral obstruction is most commonly seen in male cats because of their long, narrow urethra and susceptibility to urethral plugs from lower urinary tract disease, but it also occurs in male dogs, usually from stones lodging behind the os penis (the bone within the penis), and can affect any cat or dog. The condition can affect cats of any age but is most common in young to middle-aged males. Stress, diet, and previous episodes of lower urinary tract disease may contribute to risk. Obstructions can develop rapidly and progress quickly to a life-threatening state.
The blockage prevents urine from leaving the bladder, causing progressive bladder distension, accumulation of waste products in the blood, and electrolyte imbalances. Complete obstruction causes uraemia within 36 to 48 hours, and rising potassium can disturb the heart rhythm. The bladder becomes increasingly painful and can rupture. Without relief of the obstruction the condition is fatal: one veterinary reference gives death at about 72 hours after complete obstruction, and another states that death may come in less than 24 to 48 hours.
Signals & patterns
Early signals
Frequent visits to the litter tray
The cat repeatedly enters the litter tray, straining, but produces little or no urine.
Vocalising when attempting to urinate
Crying or meowing during litter tray visits indicates pain and distress.
Licking the genital area excessively
Cats often lick at their genitals due to discomfort and irritation.
Restlessness
Affected cats often appear uncomfortable, moving frequently and unable to settle.
Later signals
Vomiting
As waste products accumulate in the blood, nausea and vomiting develop.
Complete inability to urinate
No urine production despite repeated attempts indicates complete obstruction.
Weakness or collapse
Electrolyte disturbances, particularly high potassium, cause muscle weakness and can affect the heart.
Hiding and refusing to eat
Severely affected cats become withdrawn, stop eating, and seek secluded places.
Click to read about the biological mechanisms
How this is usually investigated
Diagnosis is typically straightforward based on physical findings. Investigation also assesses the metabolic consequences and helps plan stabilisation.
Physical examination
Blood tests
Electrocardiogram
Urinalysis
Imaging
Options & trade-offs
Relief of obstruction is the first priority, followed by stabilisation and strategies to reduce recurrence risk.
Urethral catheterisation
Passing a urinary catheter to relieve the obstruction and empty the bladder.
Trade-offs: Requires sedation or anaesthesia. The catheter is typically left in place for a few days until the urethral swelling subsides.
Intravenous fluid therapy
Fluids to correct dehydration, flush out waste products, and restore electrolyte balance.
Trade-offs: Given alongside relief of the obstruction. Cats typically require hospitalisation for fluid therapy and monitoring.
Cardiac stabilisation
Specific treatments to protect the heart when potassium is dangerously elevated.
Trade-offs: Calcium gluconate, given slowly into a vein with ECG monitoring, may be used when potassium is life-threateningly high, and glucose, alone or with soluble insulin, may be used to lower potassium. No calcium gluconate or soluble insulin product is authorised for cats in the UK, so these are human medicines used under the veterinary medicines cascade. Glucose infusions authorised for cats are available.
Dietary management
Prescription diets designed to reduce crystal formation and maintain urinary health.
Trade-offs: An important component of long-term prevention. Different diets address different crystal types.
Perineal urethrostomy
Surgery to create a permanent, wider urethral opening, reducing obstruction risk.
Trade-offs: Considered for cats with recurrent obstructions. Carries some surgical risks and changes urinary tract anatomy.
Common misconceptions
"A blocked cat can wait until morning"
Urethral obstruction progresses over hours. Complete obstruction can be fatal in less than 24 to 48 hours, and that time runs from when the blockage became complete, not from when the signs were first noticed.
"Female cats are blocked as often as males"
Urethral obstruction occurs almost exclusively in male cats, whose urethra is longer and narrower. Female cats develop lower urinary tract disease with the same straining, but obstruction in a female is rare.
"If a cat pees a little bit, they're not blocked"
Partial obstructions can still become complete, and a few drops of urine do not show that the urethra is open. Whether the bladder is emptying cannot be judged at home: a blocked bladder is found distended and painful when it is felt on examination.
Related conditions
Urinary Stones (Urolithiasis)
Urinary stones can contribute to urethral obstruction when small stones pass from the bladder into the urethra and become lodged there, particularly in male cats and dogs with a narrow urethral diameter.
Constipation and Megacolon in Cats
Constipation and urethral obstruction can appear similar to an owner, because both may cause straining in the litter tray or garden, often without producing the expected result. The two cannot be told apart reliably at home. A blocked bladder is found distended and painful when it is felt on examination, and a blocked cat taken to be constipated loses hours that count.
Hydronephrosis
Hydronephrosis can develop when urethral obstruction prevents urine from leaving the bladder, causing pressure to build and extend back up the ureters to the kidneys. The degree of swelling depends on how complete the blockage is and how long it has been present.
Prostatic Hyperplasia
Prostatic hyperplasia is a condition of intact male dogs, not cats. Many affected dogs show no signs, and blood in the urine and straining are among the signs described. Complete urethral obstruction is described with prostatic tumours. It is not listed among the signs of benign enlargement.
Feline Idiopathic Cystitis
Feline idiopathic cystitis is a common cause of urethral obstruction in male cats. The inflammation can produce a plug of proteins, cells, crystals and debris that lodges in the urethra, and the pain and irritation can send the muscle around the urethra into spasm.
Knowing litter tray habits helps recognise changes early. Observing whether a cat is producing urine (versus just posturing) and noticing any crying or distress during attempts provides important information. Straining to urinate and straining to defaecate look alike, and the two cannot be told apart reliably at home. Male cats with any history of urinary issues warrant particular attention.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS