Feline urethral obstruction

What it is

Urethral obstruction is the inability to empty the bladder because of a blockage in the urethra. In the cat it almost always affects males, and its main causes are:

• Urethral plugs: soft masses of protein matrix, inflammatory cells and often struvite crystals, which form in the setting of feline idiopathic cystitis.
• Small uroliths (calcium oxalate or struvite) passing down from the bladder.
• "Functional" or idiopathic obstruction: urethral spasm, oedema and inflammation without identifiable obstructive material.
• Less often, urethral stricture (for example after catheterisation or trauma) or neoplasia.

Because urine cannot leave, bladder pressure is transmitted to the ureters and kidneys and glomerular filtration falls: urea, creatinine, potassium and acids accumulate (post-renal azotaemia, hyperkalaemia and metabolic acidosis). Hyperkalaemia disturbs cardiac conduction and can cause bradycardia, arrhythmias and death. The overdistended bladder can rupture or lose its contractility (detrusor atony).

Who it affects

Male cats, neutered or intact, usually young to middle-aged, overweight, indoor, sedentary and fed dry food; stress and cold weather have been associated with episodes. Recurrence is common, especially in the first months after the first episode.

Anatomy involved

• Male feline urethra: long, with a diameter that decreases distally; the penile part, distal to the bulbourethral glands, is the narrowest and the usual site of obstruction. The cat's penis points caudally.
• Urinary bladder: large, firm and painful on palpation; its wall can become ischaemic from overdistension.
• Kidneys: post-renal acute kidney injury, usually reversible if the obstruction is relieved quickly.

Clinical signs

Repeated, unproductive straining in the litter box (often mistaken by owners for constipation), vocalisation, licking of the penis, which may look congested, haematuria and dribbling of urine. If the obstruction persists, vomiting, anorexia, lethargy, dehydration and, in severe cases, collapse, hypothermia and bradycardia from hyperkalaemia appear. The bladder feels large, hard and painful.

Diagnosis

• Abdominal palpation: a large, firm bladder that cannot be expressed.
• Emergency blood work: potassium, urea, creatinine, venous blood gas, ionised calcium (often low) and glucose.
• Electrocardiogram: bradycardia, tall T waves, flattened or absent P waves and wide QRS complexes in severe hyperkalaemia.
• After stabilisation: urinalysis and urine culture, radiographs of the whole urethra and ultrasound to look for uroliths and assess the bladder and kidneys.

Treatment

Stabilisation comes first: intravenous fluids, treatment of hyperkalaemia (calcium gluconate to protect the heart, insulin with glucose or bicarbonate to shift potassium into cells) and analgesia. Decompressive cystocentesis can relieve the bladder while catheterisation is prepared. Under sedation or anaesthesia the urethra is unblocked with a catheter and retrograde flushing, and an indwelling urethral catheter with a closed collection system is usually left for one or more days, monitoring the post-obstructive diuresis, which can be marked. The cause is then treated: idiopathic cystitis (increased water intake, environmental enrichment), uroliths (dissolution or removal) and infection if present. Cats with repeated obstructions or a stricture of the penile urethra undergo perineal urethrostomy, which widens the outlet but increases the later risk of urinary tract infection. Most cats treated in time survive, but the risk of recurrence is high.

Key studies

Does early neutering narrow the urethra?

It is a widespread belief, but the available evidence does not support it. No study has shown that neutering a male cat early (before or around 6 months) stops the urethra from growing or raises the risk of obstruction.

• Root et al. (1996), a controlled experimental study with 6 cats per group. Males neutered at 7 weeks, neutered at 7 months or left intact had their urethra measured by voiding cystourethrography at 22 months. The penile urethral diameter did not differ between groups. What did change was the penis: it could be fully extruded in 6 of 6 intact cats, 3 of 5 cats neutered at 7 months and 0 of 6 cats neutered at 7 weeks. This is probably the source of the confusion between an infantile-looking penis and a narrow urethra. It is a small study with little statistical power.
• Porters et al. (2015), a randomised trial of 800 kittens neutered at 8–12 weeks or at 6–8 months. There was no difference in lower urinary tract disease or urethral obstruction up to 24 months. Follow-up is short for a disease that peaks at 2–4 years.
• Spain et al. (2004), a retrospective cohort of 1660 cats followed for up to 11 years. Neutering before 5.5 months did not increase any of the serious conditions studied, urinary ones included. Howe et al. (2000) reached the same conclusion in 263 shelter cats. Both relied on owner-reported data.
• Lee et al. (2025), ultrasound of 302 cats. Urethral wall thickness was the same in neutered and intact males, although age at neutering was not recorded and there were only 13 intact males.

What is associated with obstruction is body condition. In a case-control study of 195 obstructed cats and 195 controls, each extra point of body condition score multiplied the rate of obstruction by 1.6, and the rate peaked at 2 to 4 years of age (Jukes et al., 2019). Neutering promotes weight gain, so the risk has more to do with weight control than with the age at which the cat is neutered.

Management and recurrence

• iCatCare consensus (Taylor et al., 2025): the current reference guideline for diagnosing and treating feline lower urinary tract diseases, obstruction included.
• Prazosin: two blinded trials have not shown that it reduces re-obstruction. In Reineke et al. (2017, 47 cats) it was 37% with prazosin and 31% with placebo at 6 months; in Hanson et al. (2021, 65 cats), 30% versus 18% at 30 days.
• Meloxicam: added to treatment, it did not change the re-obstruction rate in a randomised trial of 51 cats (Nivy et al., 2019). Cumulative re-obstruction was 16% at 6 months.
• Azotaemia: in 601 cats from several centres, azotaemia on admission lengthened catheterisation and resolved within 48 hours in 70% of cases. Cats with recurrent obstruction did not do worse (Skinner et al., 2026).