Feline Lower Urinary Tract Disease
Pathogenesis of Feline Urethral Obstruction
Feline urethral obstruction is a blockage of the urethra, the tube that carries urine from the bladder out of the body. Debris in the urethra, including gritty material and crystals, and in some cats bladder stones (calculi), can stop urine from leaving.
When urine cannot exit, the bladder fills and pressure builds. That pressure backs up toward the kidneys and reduces their ability to filter blood. Waste products accumulate, a state called azotemia (elevated kidney waste values in the blood).
Potassium is cleared mainly through urine, so it rises too. Hyperkalemia (high blood potassium) is the most immediately dangerous consequence because potassium disrupts the heart’s electrical activity. It can slow the heart rate (bradycardia), cause arrhythmias (abnormal rhythms), and in some cats produce a fast heart rate (tachycardia) instead.
Acid also accumulates, causing acidosis (excess acid in the blood). Together, azotemia, hyperkalemia, and acidosis explain why blocked cats become so ill: vomiting, severe lethargy, and hypothermia (low body temperature). Some cats also develop hypotension (low blood pressure).
Common client complaints
“why is my cat yowling in the litter box”
A blocked cat often cries out because the bladder is full and painful and little or no urine is passing. Yowling with straining is treated as an emergency.
“my cat keeps going to the litter box but nothing comes out”
This is straining against an obstruction. The bladder keeps filling but the blocked urethra prevents a normal stream.
“why is my cat throwing up and so lethargic”
Vomiting and extreme lethargy reflect waste products and electrolyte disturbances building up in the blood. Vomiting before presentation is a recognized sign of azotemia and hyperkalemia.
“why does my cat feel cold and weak”
Hypothermia is a recognized sign of an azotemic, hyperkalemic cat. It reflects how sick the cat has become, and heat support is part of treatment.
“my cat’s heartbeat seems really slow, is that related”
Bradycardia is a classic sign of hyperkalemia because excess potassium interferes with the heart’s electrical conduction. Some hyperkalemic cats have a rapid heart rate instead.
“why does my cat need a catheter and to stay in the hospital after being unblocked”
In the studies cited in the Prognosis section, cats unblocked and sent home immediately reblocked more often than cats kept with an indwelling urinary catheter. The catheter lets the urethra recover while the team monitors urine output and kidney recovery.
“will my cat block again”
Reblocking is a real risk after the first obstruction. Diet is the main long-term tool for reducing it, as covered under Prognosis.
Diagnostics
Any cat with yowling, straining to urinate, or extreme lethargy and vomiting is triaged quickly so the bladder can be palpated (felt through the abdominal wall). Confirmed blocked cats are then evaluated with a standard set of tests.
History. The veterinarian asks about diet type and brand, the number of cats and litter boxes in the household, and any stressful events or environmental changes in the prior week. This identifies risk factors that shape recurrence prevention and diet planning.
Bladder palpation. A large, firm, painful bladder supports the diagnosis of obstruction. It is also used to monitor whether the bladder stays small once a catheter is in place.
EPOC blood analysis. This point-of-care test measures electrolytes, acid-base status, glucose, and kidney values. It assesses severity and is run before anesthesia, because a high potassium level changes how the cat is stabilized and sedated.
Urinalysis. Evaluates urine for crystals, blood, and bacteria. If bacteria are seen, a Diff-Quik sediment stain can confirm them. Results help decide whether infection is present, which matters because antibiotics are not used without convincing evidence of infection.
EKG (electrocardiogram). Suggested before anesthesia when potassium is very high or the heart rhythm is irregular. It shows how hyperkalemia is affecting the heart, guides how aggressively potassium is treated before anesthesia, and monitors arrhythmias during treatment.
Radiographs (X-rays). At minimum, a lateral view is taken to look for stones in the bladder or urethra. Radiographs do not detect every stone, so a clear film does not fully rule out calculi. Ultrasound can add information when the bladder is full.
Urine culture. Considered at presentation for older cats, very azotemic cats, or when bacteria appear on urinalysis. A culture is also collected just before the catheter is removed. It confirms whether a true infection exists and identifies the organism.
Repeat blood glucose. After potassium-lowering treatment with insulin and dextrose, glucose is rechecked to catch low blood sugar, a known risk of that therapy.
Follow-up urinalysis and urine pH. After a diet change, a repeat urinalysis checks for struvite (a common urinary crystal) and measures urine pH. A pH that is too high may prompt a diet change to reduce struvite formation.
Treatment of Feline Urethral Obstruction
Treatment moves from stabilization to unblocking to catheter-based recovery. The priority is to correct the life-threatening electrolyte and cardiac effects, then relieve the obstruction safely.
Stabilization
Catheter placement and fluid therapy. Fluids restore circulation and dilute potassium. Balanced fluids such as Normosol-R, Plasma-Lyte, or lactated Ringer’s are preferred over 0.9% saline because acidosis improves faster with them, with similar decreases in potassium. A hypotensive cat receives a fluid bolus (a rapid initial fluid challenge) to restore blood pressure.
Calcium gluconate. Used in very hyperkalemic cats while the heart is monitored by stethoscope or EKG. It does not lower potassium. It protects the heart from potassium’s effects and can help with both slow rhythms and tachyarrhythmias.
Regular insulin with dextrose. Used when potassium is markedly elevated, especially if arrhythmias are present. Insulin drives potassium from the blood into cells, and dextrose keeps blood sugar from dropping. Because glucose can still fall afterward, dextrose is added to the fluids and blood glucose is rechecked.
Heat support. Provided when body temperature is low.
Analgesia. Methadone or fentanyl controls pain before unblocking.
Anesthesia and unblocking
Fluids run concurrently with anesthesia and unblocking. Drug choice depends on cardiovascular status. For a cat that is hyperkalemic, hypotensive, and bradycardic, options include low-dose ketamine with diazepam (Valium), or midazolam with alfaxalone. Propofol and dexmedetomidine are not recommended for hypotensive cats or cats with arrhythmias because they can further depress heart function.
A coccygeal epidural block, a local anesthetic nerve block at the base of the tail using bupivacaine, can be considered for added comfort during the procedure.
The prepuce and perineum are clipped and lightly scrubbed. The penis is flushed with a soft-tip tool, such as a catheter without a needle, an olive-tip, or a urethral catheter without its stylet. The urethra is then flushed copiously, particularly when the material is gritty, to clear debris and crystals. A soft indwelling urinary catheter is placed, connected to a closed collection system (which lowers infection risk), secured, and protected with a hard Elizabethan collar so the cat cannot remove it.
Monitoring and hospitalization
Fluid therapy is adjusted over time based on urine output and hydration. Some cats develop postobstructive diuresis (a surge in urine production after the blockage is relieved), which calls for closer monitoring of urine output, body weight, and fluid needs.
Urine output is measured so that fluids in match urine out.
Bladder palpation is repeated to confirm the bladder stays very small while the catheter is in place.
Catheter care. The collection line is wiped with dilute chlorhexidine to reduce infection risk. The catheter is flushed only if the urine is very gritty or the catheter is obstructed.
Catheter duration is guided by urine appearance, degree of azotemia, and how difficult the unblocking was.
Pain control after unblocking uses buprenorphine or methadone plus gabapentin.
Stones. If stones are seen, the catheter stays in until surgery. After cystotomy (surgical opening of the bladder), radiographs confirm that all stones were removed.
Urine culture is collected through the line just before the catheter is removed.
Medications deliberately avoided
Antibiotics are not started without convincing evidence of infection.
Prednisone is avoided because it has been shown to increase the risk of pyelonephritis (kidney infection).
Common complications
Hyperkalemia and cardiac arrhythmias. Potassium builds up when the kidneys cannot excrete it. Recognition relies on bradycardia (or sometimes tachycardia), irregular rhythms, and EKG changes. It makes anesthesia riskier, so it is treated before unblocking and monitored throughout.
Azotemia and acidosis. Obstruction reduces kidney filtration, so waste and acid accumulate. They are recognized on blood analysis and by vomiting, lethargy, and hypothermia. Severity influences fluid needs and how long the catheter stays in.
Hypotension and hypothermia. Illness and the cardiac effects of hyperkalemia can lower blood pressure and body temperature. Management includes fluid boluses, heat support, and careful anesthetic selection.
Hypoglycemia after insulin and dextrose. Insulin can drop blood sugar. It is prevented by giving dextrose and caught by rechecking glucose.
Post-obstructive diuresis. After the blockage clears, a surge in urine output can cause dehydration if fluids are not adjusted. It is recognized by high urine output and managed with closer monitoring of urine volume, weight, and fluid rate.
Reblocking. The urethra can obstruct again, sometimes while the cat is still hospitalized. It is recognized by a bladder that refills despite the catheter or a catheter that stops draining. It is a central reason indwelling catheters and monitored hospitalization are used.
Urinary tract infection and pyelonephritis. A catheter and an inflamed urinary tract raise infection risk. Catheter line hygiene, culture when indicated, and avoiding prednisone help reduce it. Antibiotics are reserved for convincing evidence of infection.
Urinary stones. Calculi seen on imaging change management: the catheter stays in until surgery, and postoperative radiographs confirm complete removal.
Prognosis
Outlook depends on how sick the cat is at presentation, how completely the obstruction is relieved, and how well the urinary tract is protected afterward. Reblocking is the central concern.
Short-term outlook
The emergency phase is more dangerous in cats with severe hyperkalemia, hypotension, bradycardia, hypothermia, and marked azotemia. Each reflects the physiologic stress of obstruction: potassium threatens the heart, and low blood pressure and temperature signal circulatory compromise. This is why stabilization comes before anesthesia and unblocking.
Recurrence risk
Published studies show a wide range of reblock rates, and they describe typical patterns, not a prediction for any individual cat:
In a study of 91 cats, 11% of cats treated with an indwelling catheter reblocked within 30 days, versus 31% of cats unblocked and sent home immediately. Urine color was associated with reblock risk.
In a study of 95 cats treated with prazosin (a drug sometimes used to relax the urethra) and an indwelling catheter, 13% reblocked within 30 days.
In a study of 65 cats, 25% reblocked within 30 days, 10 of them while still hospitalized, with no difference with or without prazosin.
In a study of 388 cats, the reblock rate at 14 days was higher with prazosin (24%) than without (13%).
These differences reflect different patient populations and treatment approaches. Taken together, an indwelling catheter with monitored hospitalization appears to lower early reblocking compared with immediate discharge.
Long-term management
Diet is the main lever for reducing recurrence.
Wet food is one of the few measures shown to lower the recurrence rate.
A urinary diet (S/D or S/O) is highly recommended in the short term after obstruction. In one study, no recurrences were seen in the year after obstruction in cats fed S/D.
For cats without struvite, a wet food from a reputable brand is the consensus. A urinary diet is considered for cats with repeat lower urinary tract signs, a history of obstruction, or obesity.
For cats with struvite, either a urinary diet or wet food can be used, with a urinalysis and pH recheck afterward. A urinary diet is recommended for cats with urethral obstruction, recurrent lower urinary tract events, or a high crystal load.
Cats that keep having problems or reblock warrant multiple-view radiographs and/or ultrasound to look for an underlying cause such as stones.