A cat's ureter is only 0.3 to 0.4 mm across. A 1.5 mm calcium oxalate stone is four times wider than the tube it has to pass through. That single ratio explains why feline ureteral obstruction behaves nothing like a bladder stone, why "wait a few days and see" often ends with a dead kidney, and why the repair costs $4,000 to $9,000 at a US referral hospital. Here are the numbers that should drive the decision.
Ureter, not urethra
The urethra runs from bladder to outside; a plug there is the classic male-cat emergency covered in the blocked male cat guide. The ureter is the much thinner pipe from kidney to bladder, and cats have two of them. In cats, 98% of ureteroliths are calcium oxalate, which no diet, urine acidifier, or dissolution protocol can shrink. That is the first hard fact: unlike struvite, this stone will not melt. The mineral difference is laid out in struvite versus oxalate stones.
Because the healthy kidney compensates, bloodwork lies for a while. Azotemia is present at presentation in 83% of cats with unilateral obstruction. Ultrasound is the practical test: a dilated renal pelvis with a shadowing stone, about 90% sensitive for calculi.
What owners actually see
Rarely the dramatic litter-box yowl. More often lethargy, appetite loss, vomiting, weight loss, and a cat that hides. Urinary signs may be absent entirely. That vagueness is why many cats arrive azotemic, not early. Ask for creatinine, phosphorus, potassium, urine specific gravity, blood pressure, and an ultrasound that measures the renal pelvis in millimetres.
Will the stone pass on its own?
The best recent number comes from 72 cats with 103 obstructed kidneys managed medically for at least 72 hours: 30% resolved. Success clustered in younger cats and small distal stones, with a median stone length of 1.85 mm in the successes. Uroliths succeeded 23% of the time; strictures and pyonephrosis did better, at 50%. A 70-cat tamsulosin series found 22 stones passed (31%), and passing stones averaged 1.09 mm vertical diameter against 1.34 mm for failures, with 62.5% of successes located distally.
Human benchmarks get quoted badly. In people, stones under 5 mm pass 75% to 98% of the time and 5 to 10 mm stones 25% to 47%, but the human ureter is 6 to 8 mm wide, roughly 15 to 20 times the feline lumen. Proportionally, a 2 mm stone in a cat is a 30 to 40 mm stone in a person. The practical translation: a distal stone of 1 to 2 mm in a cat that is eating, urinating, and only mildly azotemic can be watched for 24 to 72 hours with repeat creatinine and ultrasound. Anything larger, anything proximal, or any cat that is vomiting and withdrawn goes to intervention.
The four-day window
Experimental work summarized by MSPCA-Angell gives the cleanest timeline. After complete unilateral obstruction, glomerular filtration rate returns to normal if the blockage is relieved within 4 days. Renal blood flow falls to about 20% of normal by 2 weeks, and after 2 weeks filtration rate stays below 50% of normal even when urine flow is restored. Partial obstruction is more forgiving, but damage still accumulates.
The clinical mirror is a 2026 study of azotemic cats: those whose creatinine fell at least 50% by 48 hours after decompression had a median survival of 989 days, against 225 days in cats that did not. The first two days of treatment are a prognostic test, not just a drip.
Three routes to a working kidney
| Route | What it involves | Discharge and survival | Main long-term problem |
|---|---|---|---|
| Open ureterotomy or neoureterocystostomy | Cut the ureter or reimplant it into the bladder under general anesthesia, with a 0.4 mm lumen to suture | Reported morbidity 13% to 30%, mortality 8% to 20% | Re-obstruction 22% to 40% |
| Double-pigtail stent | A stent threaded from bladder to kidney, placed surgically or by cystoscopy | Perioperative complications 10% to 14% | Dysuria 17% to 35%, urinary infection 20%, re-obstruction 22%, migration 5% |
| SUB device | Nephrostomy and cystostomy catheters joined to a port under the skin | 93.8% discharged, median survival 827 days | Luminal obstruction 17%, infection 24% to 26% |
What a SUB device is, day to day
Two catheters, one curled into the renal pelvis and one into the bladder, meet at a Y connector and drain into a port sutured under the abdominal skin. The port is the point of the design: a nurse can flush it with a non-coring needle without sedation. Most centers flush at 1 week and 1 month, then every 3 to 6 months; mineralized devices are sometimes irrigated with tetrasodium EDTA. Expect kinking in 3% to 10%, luminal mineralization in 17% to 25%, and chronic infection in 24% to 26%. One 40-cat cohort reported a 48% major complication rate, most managed medically but some needing revision; a separate 81-cat series found luminal obstruction in 18 of 109 devices.
The bill, and what drives it
US referral hospitals quote roughly $4,000 to $9,000 for SUB placement. The low end assumes an uncomplicated two-to-three-day stay; the high end includes ICU days and complications. Budget separately for year one: rechecks with creatinine and ultrasound at 1 month, 3 months, and 6 months, then twice yearly, plus flushes at each visit. Outside the US, prices are set locally, so ask for an itemized written estimate before consenting.
Survival is not the same as a normal kidney
In the largest published series, 93.8% of cats left hospital, 90% were alive at 1 month, 83% at 3 months, 80% at 6 months, and 74% at 1 year, with a median survival of 827 days. Of the whole group, 51% eventually died, and 27.6% of those deaths were attributed to a renal cause. Persistent azotemia after surgery is common; stage it properly with IRIS staging and expect the contralateral kidney to be the long-term limiting factor. Pre-existing kidney disease, bilateral obstruction, or a creatinine that refuses to fall all worsen the outlook.
When to go tonight
A cat that stops eating for more than 24 hours, vomits repeatedly, hides, or is found to have a dilated renal pelvis should be referred the same day, not next week. If the cat is male, straining, and producing no urine at all, that is urethral obstruction — a separate emergency with a 24 to 48 hour clock.
This article is for orientation and does not replace a veterinary diagnosis. Obstruction, stone size, and surgical options have to be assessed in person, with imaging and bloodwork, by the veterinarian who can act on them.
Terms mentioned in this article
Frequently asked
How long can a cat survive with a ureteral obstruction?
Days, not weeks, if the blockage is complete. Filtration rate can return to normal when the obstruction is relieved within 4 days; by 2 weeks renal blood flow is roughly 20% of normal and filtration stays under 50% even after relief. A creatinine drop of at least 50% within 48 hours of decompression is associated with a median survival of 989 days versus 225 days without it.
Can a ureteral stone dissolve with a prescription diet?
No. About 98% of feline ureteroliths are calcium oxalate, which cannot be dissolved by diet, urine acidification, or any dissolution protocol. That is the main difference from struvite bladder stones, which can sometimes be dissolved. The only routes are spontaneous passage, medical management with fluids and ureteral relaxants, or surgery and stenting.
Is the SUB device permanent, and what maintenance does it need?
It is designed to stay in place for life. The port under the skin is flushed at about 1 week and 1 month after placement, then every 3 to 6 months, usually without sedation. Expect device problems over time: kinking in 3% to 10%, luminal mineralization in 17% to 25%, and infection in roughly a quarter of cats, with some devices needing revision or replacement.