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DISEASE · CATS

Urinary blockage in cats: signs, blood work and outlook

A blocked cat cannot empty his bladder. Waste products and potassium build up in the blood, and a high potassium can stop the heart. It happens almost only in male cats. It is an emergency, but most cats treated in time go home.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

A male cat that strains in the litter box and passes little or no urine needs a vet the same day. At presentation, most blocked cats have high kidney values, and about half have a high potassium and a low ionized calcium. About 1 cat in 8 has a severe, life-threatening mix of high potassium, acid blood and low calcium. In referral hospitals, about 9 cats in 10 survive the episode, but a blockage comes back in roughly a quarter to a third of cats.

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Why a blocked cat is an emergency

Urethral obstruction happens almost only in male cats, because their urethra is long and narrow [1]. The cat goes to the litter box again and again, strains, may cry out, and passes only drops or nothing. The bladder becomes large and firm [6].

When urine cannot leave the body, the kidneys stop clearing waste and potassium [10, 11]. In one study of 82 blocked cats, 58% had stopped eating, 23% were vomiting, 51% had a low body temperature, and 15% were in shock [1]. A slow heart rate together with a low temperature strongly suggests a very high potassium [4].

What causes the blockage

CauseWhat it isTo know
Idiopathic (no cause found)Inflammation and spasm of the urethra, often linked to idiopathic cystitis24 of 45 blocked cats in a Swiss study [2].
Urethral plugA soft plug of protein, cells and crystals (often struvite)8 of 45 cats in the same study; older US studies found plugs in 42–59% [2].
Stones (uroliths)A small stone stuck in the urethra13 of 45 cats; X-rays help find them [2].

Among cats with lower urinary tract disease, idiopathic disease is the most frequent diagnosis, and 58% of 77 such cats were blocked at presentation [9]. Indoor life, low water intake and extra body weight are risk factors [6]. Blocked cats were younger and heavier than other cats, and more often ate only dry food [1]. Idiopathic cystitis is explained in urinary tract infections in dogs and cats.

What the blood work shows at presentation

  • Kidney values (creatinine, BUN): high in 85% of blocked cats; median creatinine 4.43 mg/dL [1]. This is a post-renal azotemia: the kidneys cannot get rid of waste because urine cannot leave [11]. See creatinine and BUN in cats.
  • Potassium: high in 48% [1], and severely high (above 8.0 mmol/L) in 12% of 199 cats in a larger study [3]. A high potassium can cause heart rhythm problems and even cardiac arrest [10]. See potassium in dogs and cats.
  • Acid blood (acidosis): 79% of cats with severe high potassium also had a blood pH below 7.20 [3].
  • Ionized calcium: low in 56% [1]. In cats with severe high potassium, 75% also had an ionized calcium below 1.0 mmol/L [3]. Low calcium may add to heart problems [12].
  • Sodium: low in 55% [1].
  • Blood count: a high white cell count in 41% and a high hematocrit in 35% [1].

The higher the creatinine, the higher the potassium tends to be [1, 3]. Most blocked cats have only mild changes, but about 12% have several life-threatening changes at once [3].

How to read the potassium line

Here is an example line from a male cat that has been straining in the litter box since the day before.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
K Potassium8.4mmol/L3.5–5.5H
  1. Abbreviation K, K⁺ or potassium, in the electrolyte block with sodium (Na) and chloride (Cl).
  2. Result 8.4 mmol/L in this illustrative line: severely high. Above 8.0 mmol/L was classed as severe in a study of 223 blocked cats [3].
  3. Unit mmol/L or mEq/L: the same number for potassium [10].
  4. Laboratory interval The interval used in a study of blocked cats; each laboratory sets its own [1].
  5. Flag H: above the interval. With a blocked bladder, it calls for emergency care, because a high potassium can disturb the heart rhythm [10]. Ionized calcium and blood pH are checked at the same time [3].

Urinalysis and urine culture

  • Blood in the urine: found in all cats tested on the dipstick, and protein in 88% [1]. The dark color of the urine can make the dipstick misleading [1].
  • Sediment: white cells in 65% and struvite crystals in 39% of the cats checked [1].
  • Urine concentration: median specific gravity 1.025 [1].
  • Culture: in 34 blocked cats sampled by needle from the bladder, none had bacteria at presentation [7]. A urinary catheter can bring bacteria in: 13% of cats grew bacteria during catheterization [7]. Routine antibiotics are not recommended; a culture guides the choice [6].
  • X-rays or ultrasound look for stones and check the bladder and kidneys [1, 2].

See urinalysis in dogs and cats for how each line of the urine report is read.

Survival, recovery and recurrence

In referral hospitals, 90–95% of blocked cats survive [6]: 93.6% of 219 cats in one study [3], and 91.5% (8.5% did not survive) in another [1]. Cats were hospitalized for a median of 3.5 days, and most went home with a normal creatinine: only 10.3% were discharged with a creatinine above the reference interval [1]. Cats that died had a lower ionized calcium at presentation [1].

A blockage often comes back. Reported recurrence is 15–40% [6]: 11% within 24 hours and 24% within 30 days of catheter removal in 192 cats [5], and 22% within 6 months in another study [1]. In the Swiss study, 36% blocked again and 51% had urinary signs again, whatever the cause [2]. A surgery that widens the urethra (perineal urethrostomy) is used for some cats that keep blocking [1]. Drinking more water and changes to the cat’s environment seem to lower the risk [6].

In UK general practice, 29.6% of 1,108 blocked cats died during the episode, and 88% of these deaths were euthanasia [8]. In the Swiss study, 21% of cats were later euthanized, most often because the blockage came back [2]. Lower-cost hospital protocols have been studied for some cats as an alternative to euthanasia when finances are limited [13].

Related articles

Potassium in dogs and cats

Why a high potassium is dangerous for the heart.

Read the article

Creatinine and BUN in cats

The kidney values that rise when urine cannot leave.

Read the article

Urinalysis in dogs and cats

Blood, protein, crystals and specific gravity.

Read the article

If the kidney values stay high after the blockage is relieved: kidney disease in cats.

En français : chat bouché (obstruction urinaire).

Questions to ask your veterinarian

  1. How high is the potassium, and is the heart rhythm affected?
  2. How high are the creatinine and BUN, and when will you recheck them?
  3. Are the ionized calcium and blood pH abnormal?
  4. Did the X-rays or ultrasound show a stone, and is a urine culture needed?
  5. What is the risk that he blocks again, and what can we change at home?
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Frequently asked questions

Is it possible for a cat to survive a urinary blockage?

Yes. With emergency treatment, 90–95% of blocked cats survive in referral hospitals [6]. Without treatment, high potassium and kidney failure can be fatal [10, 11].

How long does it take a cat to recover?

In one study, blocked cats stayed in hospital for a median of 3.5 days, and most went home with a normal creatinine [1]. The first weeks matter: about 1 cat in 4 blocked again within 30 days [5].

Do people put cats down for urinary blockage?

Sometimes. In UK general practice, 29.6% of blocked cats died during the episode, mostly by euthanasia [8]. In a Swiss study, 21% were euthanized later, most often because the blockage came back [2]. Most cats treated in hospital survive [3, 6].

What is the most common cause of urethral obstruction in cats?

In recent studies, most often no cause is found (idiopathic), often linked to idiopathic cystitis: 24 of 45 cats in one study [2]. Plugs and stones are the other main causes [2, 6].

Can female cats get a urinary blockage?

It is rare. Urethral obstruction occurs almost only in males, whose urethra is long and narrow [1].

Sources

  1. Segev G et al. Urethral obstruction in cats: predisposing factors, clinical, clinicopathological characteristics and prognosis. J Feline Med Surg. 2011;13(2):101-108. doi.org/10.1016/j.jfms.2010.10.006
  2. Gerber B, Eichenberger S, Reusch CE. Guarded long-term prognosis in male cats with urethral obstruction. J Feline Med Surg. 2008;10(1):16-23. doi.org/10.1016/j.jfms.2007.06.007
  3. Lee JA, Drobatz KJ. Characterization of the clinical characteristics, electrolytes, acid-base, and renal parameters in male cats with urethral obstruction. J Vet Emerg Crit Care. 2003;13(4):227-233. doi.org/10.1111/j.1534-6935.2003.00100.x
  4. Lee JA, Drobatz KJ. Historical and physical parameters as predictors of severe hyperkalemia in male cats with urethral obstruction. J Vet Emerg Crit Care. 2006;16(2):104-111. doi.org/10.1111/j.1476-4431.2006.00189.x
  5. Hetrick PF, Davidow EB. Initial treatment factors associated with feline urethral obstruction recurrence rate: 192 cases (2004-2010). J Am Vet Med Assoc. 2013;243(4):512-519. doi.org/10.2460/javma.243.4.512
  6. Cooper ES. Controversies in the management of feline urethral obstruction. J Vet Emerg Crit Care. 2015;25(1):130-137. doi.org/10.1111/vec.12278
  7. Cooper ES et al. Incidence of bacteriuria at presentation and resulting from urinary catheterization in feline urethral obstruction. J Vet Emerg Crit Care. 2019;29(5):472-477. doi.org/10.1111/vec.12870
  8. Beeston D et al. Occurrence and clinical management of urethral obstruction in male cats under primary veterinary care in the United Kingdom in 2016. J Vet Intern Med. 2022;36(2):599-608. doi.org/10.1111/jvim.16389
  9. Gerber B et al. Evaluation of clinical signs and causes of lower urinary tract disease in European cats. J Small Anim Pract. 2005;46(12):571-577. doi.org/10.1111/j.1748-5827.2005.tb00288.x
  10. eClinPath, Cornell University College of Veterinary Medicine. Potassium. eclinpath.com/chemistry/electrolytes/potassium
  11. eClinPath, Cornell University College of Veterinary Medicine. Azotemia. eclinpath.com/chemistry/kidney/azotemia
  12. Drobatz KJ, Hughes D. Concentration of ionized calcium in plasma from cats with urethral obstruction. J Am Vet Med Assoc. 1997;211(11):1392-1395. pubmed.ncbi.nlm.nih.gov/9394887
  13. Cooper ES et al. A protocol for managing urethral obstruction in male cats without urethral catheterization. J Am Vet Med Assoc. 2010;237(11):1261-1266. doi.org/10.2460/javma.237.11.1261

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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