Kidney Stones – Tanya's Comprehensive Guide to Feline Chronic Kidney Disease

Overview

Kidney stones are stones formed from minerals that lodge in the kidneys.
They may cause CKD, and they also increase the risk of kidney infections.
If the cat’s body attempts to pass them, they may get stuck in the ureter and cause a medical crisis.
They can be difficult to treat, but there are a number of newer treatments available at a few centres which are much more promising, though unfortunately they are very expensive..

The Urinary Tract and Different Types of Urolith

I sometimes hear from people who think their cats have kidney stones but they actually have another type of problem, so I shall start by trying to explain a bit more about the urinary tract and what sort of problems may arise.

The urinary tract consists of:

two kidneys
two ureters: thin tubes, each of which leads from a kidney to the bladder
the bladder
the urethra, a tube which carries urine from the bladder to outside the body

The kidneys and ureters are considered to be the upper urinary tract and the bladder and urethra are considered to be the lower urinary tract.

One of the kidneys’ functions is to filter waste products. Unfortunately sometimes this process doesn’t work as well as it should and calculi or uroliths (stones) form somewhere in the urinary tract. The medical term for this is urolithiasis.

There are two main types of uroliths commonly seen in cats. The cat’s urine pH may give you a clue as to which type of stone you are dealing with. A normal urine pH level is in the range of 6.0 – 6.5.

Struvite

A cat with a urine pH higher than normal (i.e. more alkaline urine) can be at risk of developing struvite crystals. These may be found in the bladder (when they may be referred to as bladder stones) or the urethra. In either case, they are in the lower urinary tract, thus struvite crystals belong to the category of conditions known as feline lower urinary tract disease (FLUTD).

In some cases, struvite crystals can be dissolved with a change of diet, which may also prevent them from reappearing. Therapeutic diets are available which are acidified to change the balance of the urine so struvite crystals are less likely to develop. Many non-therapeutic diets are also acidified these days to help prevent struvite but this may be one factor in the increased incidence of calcium oxalate stones in cats (see below).

In more severe cases, where the urethra is blocked because of struvite crystals, the cat will need surgery to unblock him (cats with this type of blockage are usually male). During the period of the blockage, the cat may suffer from acute kidney injury, but with luck this will resolve once the blockage has been removed.

It is rare for CKD cats to develop problems with struvite because CKD cats tend towards acidity.

This page does not discuss struvite any further but there are some links here.

Calcium Oxalate

A cat with a lower urine pH than normal (i.e. more acidic urine) can be at risk of developing calcium oxalate stones. These may also be found in the bladder, but are also often found in the kidneys so may be referred to as renal calculi or nephroliths, or kidney stones.

The rest of this page focuses on calcium oxalate stones found in the kidneys and ureters.

Cornell University College of Veterinary Medicine has a good overview of both struvite and calcium oxalate uroliths.

Cornell University College of Veterinary Medicine also has photos of the different types of stones and crystals that may be seen.

Urolithiasis in small animals (2025) Van Vertloo L MSD Veterinary Manual discusses the different types of stones seen in dogs and cats.

Why Kidney Stones Are A Problem

In over 90% of cases, stones that form in the kidneys are calcium oxalate stones, i.e. formed from a combination of calcium and oxalate. Other, rarer stones are occasionally found, but struvite is not found in the kidneys. The stones may calcify, though some cats may develop calcified blood clots rather than actual stones.

The presence of kidney stones increases the risk of kidney infections (pyelonephritis), and may cause CKD.

Many kidney stones are inactive (static) so they do not cause any problems and you may not even know your cat has them. However, problems may arise if the cat’s body attempts to pass the stones (active) through the ureter (the tube that connects the kidney to the bladder) and down into the bladder.

Smaller stones, although painful, may be successfully passed, though it may take some time (one cat on Tanya’s Support Group took fifteen months to pass a stone).

Some stones may move into the ureter, then back into the kidney. This is less serious but may still cause kidney damage.

The main problem arises when large kidney stones start actively moving into the ureter. Since the ureter is very narrow (around 0.3mm in a cat, less than a quarter of an inch; for comparison, Cats kidney stones: a big problem with a tiny solution (2014) The University of Illinois at Urbana-Champaign College of Veterinary Medicine points out that the metal used in a paper clip is around 1mm thick), larger stones may lodge in the ureter (i.e. get stuck). This is called obstructive nephropathy or a blockage. This is very serious because it prevents waste products that would normally be filtered by the kidneys into the ureters and then excreted via the bladder from being excreted, so they build up in the kidneys. This can cause acute kidney injury.

Stones in the kidneys are called nephrolithiasis. Stones in the ureter are called ureterolithiasis.

Mar Vista Vet has a helpful overview of kidney stones.

Calcium oxalate crystalluria (2008) Haak CE & Cohn LA NAVC Clinician’s Brief Sept 2008 pp27-28 has an overview of calcium oxalate stones.

The University of Minnesota College of Veterinary Medicine Urolith Center will analyse feline stones free of charge.

Causes

Kidney stones may form if there is reduced urination for some reason, or if the urine contains more of the substances contained in the stones (in over 90% of cases, calcium and oxalate) than usual.

Urine that is more acidic (pH below 6) increases the risk of developing calcium oxalate stones. The recent trend for acidifying cat food (which is done to prevent the opposite problem of struvite crystals, which develop in urine that is too alkaline) is thought to be a factor in some cases. Magnesium levels are often reduced in cat foods in order to reduce the risk of struvite crystals and Urolithiasis in small animals (2013) Brown SA Merck Veterinary Manual states “Common management schemes that involve feeding urine-acidifying diets with reduced magnesium have reduced the incidence of feline struvite urolithiasis. Magnesium has been reported to be an inhibitor of calcium oxalate formation in rats and people; thus, the reduced magnesium concentration in feline urine may partially explain the increase in calcium oxalate stones in cats.”

Many cats with calcium oxalate stones also have idiopathic hypercalcaemia (elevated calcium levels in the blood with no obvious cause). Urolithiasis in small animals (2025) Van Vertloo L MSD Veterinary Manual says “Hypercalcemia is an important risk factor for calcium oxalate stones in cats. A notable percentage of cats with idiopathic hypercalcemia develop urolithiasis.” In fact, The utility of clinicopathological findings and point-of-care ultrasound in increasing the index of suspicion of ureteral obstruction in azotaemic cats presenting to the emergency room (2023) Beeston D, Dirrig H & Cole L Journal of Small Animal Practice 64(12) pp781-787 states “Cats with ionised hypercalcaemia were 83.4 times more likely to have ureteral obstruction than non-obstructive disease.” It is not yet known which comes first, the hypercalcaemia or the kidney stones.

Association between serum fibroblast growth factor and blood calcium levels in chronic kidney disease cats with upper urolithiasis (2022) Miyakawa H, Hsu HH, Ogawa M, Akabane R, Miyagawa Y & Takemura N Journal of Feline Medicine and Surgery 24(12) pp1245-1252 found that increased FGF-23 levels were associated with hypercalcaemia in cats with both CKD and kidney stones.

Occasionally, calcium oxalate stones may be caused by a vitamin B6 deficiency.

Certain breeds appear to be more likely to develop calcium oxalate stones, including Persian, British Shorthair, Ragdolls and Scottish Fold cats. Urolithiasis in small animals (2025) Van Vertloo L MSD Veterinary Manual says “Longhaired cats are predisposed to calcium oxalate stones, but any breed can be affected.”

Calcium in food does not contribute to the development of kidney stones. In fact, calcium in foods can bind with oxalate and therefore help prevent the formation of kidney stones. However, calcium supplements may contribute to the problem.

Symptoms

Kidney stones can be very painful but in some cases, there may be no obvious signs, since cats instinctively try to hide pain. In other cases the cat may be subdued and lethargic and not want to eat. Some cats will have blood in the urine (haematuria) or frequent kidney infections.

Some cats urinate more, but others exhibit reduced urination. If your cat is unable to urinate, this is a medical emergency and you need to get to a vet as quickly as possible.

Diagnosis

Blood Tests

Your vet will usually run blood tests. If a cat’s kidney values suddenly become extremely high, a kidney stone blocking a ureter may be the cause.

A cat with active kidney stones may also have elevated phosphorus and potassium levels.

Around 48% of cats with kidney stones will be anaemic, perhaps because of concurrent kidney disease, infection or inflammation.

A cat with big kidney little kidney (see below) may have kidney values that wax and wane.

Diagnostic imaging of urinary tract calculi (2017) VanderHart D Clinician’s Brief explains more about using x-rays and ultrasound to diagnose kidney stones.

Palpation and X-Rays

Your vet will also palpate (feel) your cat’s kidneys, which may be tender to the touch. Sometimes the vet can feel a difference in size, in which case an ultrasound will usually be performed. X-rays should be performed, and may help the vet assess the number and size of the stones.

Ultrasound

Stones may be visible on ultrasound, though this is not always the case. Bloodstones are often not visible on ultrasound. Ultrasonography in the diagnosis and management of cats with ureteral obstruction (2018) Lamb CR, Cortellini S & Halfacree Z Journal of Feline Medicine and Surgery 20(1) pp15-22 states “Ultrasonography may be used to identify azotaemic cats at greatest risk of ureteral obstruction, but when using pyelography as the reference test ultrasonography appears to be inaccurate for diagnosis of ureteral obstruction.”

However, The utility of clinicopathological findings and point-of-care ultrasound in increasing the index of suspicion of ureteral obstruction in azotaemic cats presenting to the emergency room (2023) Beeston D, Dirrig H & Cole L Journal of Small Animal Practice 64(12) pp781-787 found that ultrasound “is a useful test in azotaemic cats and finding renal abnormalities such as asymmetry, pelvic dilation and ureteral dilation should raise suspicion of ureteral obstruction and prompt discussion of further assessment and possible referral.”

An ultrasound may show dilation of the ureter and renal pelvis (the upper end of the ureter). Dilation of the renal pelvis is called pyelectasia, but Feline abdominal ultrasonography: What’s normal? What’s abnormal? Renal pelvis, ureters and urinary bladder (2020) Griffin S Journal of Feline Medicine and Surgery 22(9) pp847-865 states “The term pyelectasia is used to describe mild or moderate, non-obstructive dilation of the renal pelvis, whereas the term hydronephrosis is typically reserved for pelvic dilation secondary to obstruction, which is often much more severe.” The study adds “as expected, the most severe cases of pelvic dilation occurred in cats with urinary outflow obstruction, with diameters up to 39.1mm reported.”

Hydronephrosis means fluid build up in the kidney, which may be caused by kidney stones. Pet MD has some information about hydronephrosis, as does Pet Place.

You may see one small kidney and one enlarged kidney, known as big kidney little kidney syndrome. What this usually indicates is that a stone previously moved into one ureter, blocking it, but the cat did not exhibit any symptoms. This kidney gradually ceased to function and shrank (i.e. became the little kidney). The remaining kidney had to take over some of its work, so it grew in size (i.e. became the big kidney). If a stone eventually also moves from the big kidney into the ureter, the cat is then in crisis, because the one working (big) kidney is no longer able to function.

Some cats with big kidney little kidney syndrome will be unable to urinate, which is a medical emergency and you need to get to a vet as quickly as possible. See below for treatment options.

Feline big kidney, little kidney: acute kidney injury in the cat (2015) Costello M Presentation to the World Small Animal Veterinary World Congress discusses cats who develop big kidney little kidney syndrome and acute kidney injury secondary to kidney stones.

Evaluation of preoperative ultrasonographic parameters to predict renal recovery in long-term survivors after treatment of feline ureteral obstructions 2012-2019 (2021) McEntee EP, Berent AC, Weisse C, Le Roux A & Lamb K Journal of Feline Medicine and Surgery 24(4) pp328-336 found that “Renal appearance on ultrasound alone should not guide decisions on whether decompression will improve long-term renal outcome. As hypothesized, no preoperative imaging characteristics were found to be clinically significantly associated with long-term renal recovery.”

Treatments

There are a number of different treatments, and which one to use depends upon how severe your cat’s case is, including whether there is a blockage and, if so, whether both kidneys are affected.

Inactive kidney stones are not normally treated in cats, not even in CKD cats. Don’t worry if your vet suggests this approach because ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 state that “The presence of nephroliths in cats with chronic kidney disease did not significantly affect the progression of renal disease.” The cat should be monitored via urinalysis (to make sure the cat has not developed pyelonephritis) and x-rays every few months (to see if the stones have moved).

If treatment is required, the treatment options fall into these categories:

ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 list the various treatment options available in order of preference. These recommendations assume that every possible treatment is freely available where you live, which of course is not always the case.

How I approach…ureteral obstruction in dogs and cats (2013) Berent A Veterinary Focus 23(3) pp17-25 has an overview of the various treatment options.

University of Minnesota College of Veterinary Medicine Minnesota Urolith Center discusses kidney stones and their treatment.

Medical Management

If you cannot afford the expensive interventional treatments described below, you may have to settle for medical management of your cat’s stones. Do not give up hope if this is the case. How I approach…ureteral obstruction in dogs and cats (2013) Berent A Veterinary Focus 23(3) pp17-25 says that medical management is “effective in some feline cases (8-17%)” and recommends that it should be considered for 24-48 hours before any more invasive treatment is instigated. Dr Berent adds “During these few days of stabilization, there is a possibility that the ureterolith may pass spontaneously, making an intervention unnecessary.”

A few members of Tanya’s CKD Support Group have successfully managed their cats’ stones using medical management only.

Painkillers

Active kidney stones can be extremely painful, so discuss the use of painkillers with your vet.

Intravenous Fluids (Diuresis)

The vet uses intravenous fluids to try to flush out the stones. The cat will be hospitalised for 2-3 days and other treatments may also be offered, such as those listed immediately below.

The fluids used will not be lactated ringers solution (LRS), because this contains calcium. Normosol-R is a possibility.

How successful diuresis is depends upon a variety of factors, including the size of the stone and how long it has been in the ureter. Calcified blood clots can often be dislodged, but fewer than 10% of kidney stones are passed.

Diuretics

Sometimes diuretics such as furosemide (Lasix) or mannitol are used to increase the flushing effect and help force the stone out. ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 recommend that mannitol should be used in conjunction with IV fluids.

The recommendations also mention using thiazide diuretics for cats with frequently recurring stones.

Relaxants

Medications may also be given to relax the ureter in the hope that this will help the stone to pass through. Commonly used medications for this purpose are amitriptyline and prazosin, a muscle relaxant.

Amitriptyline eliminates calculi through urinary tract smooth muscle relaxation (2003) Achar E, Achar RAN, Paiva TB, Campos AH & Schor N Kidney International 64 pp1356–1364 discusses the use of amitriptyline in this manner in cats.

Mar Vista Vet has some information about amitriptyline.

One cat on Tanya’s Support Group who was given prazosin for six weeks managed to pass the stones and lived for a further 20 months, see Success Stories.

However, Prazosin administration increases the rate of recurrent urethral obstruction in cats: 388 cases (2022) Conway DS, Rozanski EA & Wayne AS Journal of the American Veterinary Medical Association 260(S2) S7-S11 found that cats with an obstruction who were given prazosin were more likely (24%) to reblock within 14 days of discharge than cats who were not given prazosin (13%). The study concludes “Without specific indications, the use of prazosin for the prevention of rUO [recurrent urethral obstruction] should be discouraged.”

Antibiotics

It is wise to give antibiotics to a cat in an acute situation with kidney stones. How I approach…ureteral obstruction in dogs and cats (2013) Berent A Veterinary Focus 23(3) pp17-25 says “Note that many patients with ureteral obstructions have concurrent UTI, and broad-spectrum antimicrobial therapy is recommended for all patients, with urine culture and sensitivity testing part of the work-up.”

Dietary Changes

If your cat is not in crisis, your vet may initially suggest dietary changes. Unlike struvite crystals (see above), calcium oxalate stones cannot be dissolved through a change in diet but there are a few things you can try that may help maintain your cat.

As it happens, most therapeutic kidney diets are also suitable for cats with calcium oxalate stones, whether or not they have CKD. There is a list of therapeutic kidney diets here but check with your vet that the one you wish to use is suitable.

If, on the other hand, you are feeding an acidified food (these foods are often labelled “for urinary tract health”), stop immediately. These foods are intended to treat the opposite problem to calcium oxalate stones, and can therefore make the problem worse by making the urine even more acidic. You should not give your cat anything containing cranberries for the same reason. Acidified foods are not normally appropriate for CKD cats in any event.

Pet food safety: sodium in pet foods (2008) Chandler ML Topics in Companion Animal Medicine 23(3) pp148-53 states that “Increased dietary sodium increases urine output and may decrease the risk of forming calcium oxalate uroliths due to the decrease in relative supersaturation of solutes. However, caution should be used in increasing the sodium intake of patients with renal disease as increased dietary sodium may have a negative effect on the kidneys independent of any effect on blood pressure.” Do not increase your cat’s sodium intake without your vet’s approval.

Oxalate degradation by intestinal lactic acid bacteria in dogs and cats (2004) Weese JS, Weese HE, Yuricek L & Rousseau J Veterinary Microbiology 101(3) pp161-6 mentions that the use of prebiotics, including fructooligosaccharide products (FOS), a type of fermentable fibre, may help reduce the formation of calcium oxalate stones. However, fermentable fibre may lead to elevated calcium levels in the blood (hypercalcaemia), which can itself be a risk factor for kidney stones.

If your cat needs a potassium supplement, potassium citrate (which is the type of potassium commonly found in therapeutic kidney diets) is the best choice for cats with calcium oxalate stones. Citrate to prevent calcium and uric acid stones (2014) Coe F The University of Chicago Kidney Stone Guidebook explains more about the use of citrate for this purpose in humans. ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 say “Consider potassium citrate or other alkalinizing citrate salts for dogs and cats with persistently acidic urine.”

University of California at Davis College of Veterinary Medicine has some information on the dietary management of stones.

Surgical Management

Surgery

A number of possible invasive surgeries are available, such as opening up the kidney and removing the stones, or removing a kidney or a ureter. This is very expensive (it costs several thousand dollars) and invasive. It has a relatively high mortality rate, and the stones often recur.

The use of nephroscopy and ureteral tertograde hydropulsion for urolith removal fron the upper urinary tract in 11 patients (2014) Buttin P, Collard F, Cachon T, Fau D, Goy-Thollot I, Carozzo C & Viguier E Revue de Médecine Vétérinaire 165 pp1-2, 2-11 reviewed the cases of nine cats and two dogs treated between 2008 and 2011 and found the mortality rate was 18.8% even before discharge from hospital. How I approach…ureteral obstruction in dogs and cats (2013) Berent A Veterinary Focus 23(3) pp17-25 says about ureterotomy (cutting into a ureter) “In cats, the procedure-associated complication and mortality rates are reported to be over 30% and 18%, respectively.”

In almost all cases, a stent or a subcutaneous ureteral bypass (see below) would be a better choice.

Extracorporeal Shock Wave Lithotripsy

I am sometimes asked whether this treatment is an option for cats. Extracorporeal shock wave lithotripsy (ESWL) uses shock waves to smash the stones so they can be passed. This non-invasive treatment works well in humans, and a small number of facilities in the USA do now offer this treatment for dogs, for whom it can also work well.

ESWL is only suitable if the stones are large enough to be seen on ultrasound, which unfortunately is not usually the case with cats: How I approach…ureteral obstruction in dogs and cats (2013) Berent A Veterinary Focus 23(3) pp17-25 says “This procedure can be safely performed for nephroliths <10 mm and ureteroliths <5 mm; however, because the fragments are rarely less than 1 mm, and the feline ureter is 0.3 mm in diameter, this is not an effective treatment for cats.”

Ohio State University College of Veterinary Medicine has a FAQ sheet about lithotripsy and says “All male cats and most female cats will not be large enough to have the surgery performed.” (I do wonder if male and female are the wrong way round in that sentence).

Percutaneous Nephrolithotomy (PNLE)

This is an endoscopic (keyhole) treatment for stones that are too large for lithotripsy. ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 state “In human medicine, endoscopic nephrolithotomy is the most effective minimally invasive treatment option for large stone burdens and has the highest stone-free rate when compared to alternative therapies. Endoscopic nephrolithotomy has been successfully performed in dogs and cats.” Although a cat’s size is not an issue here as it is with ESWL — How I approach…ureteral obstruction in dogs and cats (2013) Berent A Veterinary Focus 23(3) pp17-25 says “we have performed this technique on a dog weighing 3.1 kg” — I don’t know anyone who has had this performed on a cat. I think this is probably offered more to dogs.

The Animal Medical Center in NYC has some information about this procedure.

Interventional Management

Interventional treatment methods still require surgery but are much less invasive and more likely to be successful with fewer complications. Unfortunately these treatments are really, really expensive.

The Animal Medical Center has some information about these devices.

The American Society of Veterinary Nephrology and Urology gives locations throughout the world where these procedures are available.

Stent

A stent is a mesh-like tube, ideally with double pigtails at the ends to hold it firmly in place, which is placed inside the ureter. The stent causes passive dilation of the ureter.

A cat’s ureter is around 0.3mm in diameter, but an Animal Medical Center case study states that once a stent is in place for up to two weeks, the diameter can increase to up to 1.5mm. This means that the urine can flow around the stones, and in some cases (depending upon the size of the stones), it may be possible for the stones to be passed.

The cat will usually be in hospital for several days after stent placement and will usually be fitted with a feeding tube at the same time, which will remain in place for 6-12 weeks.

Outcome in cats with benign ureteral obstructions treated by means of ureteral stenting versus ureterotomy (2016) Culp WNT; Palm CA, Hsueh C; Mayhew PD; Hunt GB; Johnson EG & Drobatz KJ Journal of the American Veterinary Medical Association 249(11) pp1292-1300 looked at the use of a stent versus ureterotomy (surgical removal of the ureter). The study found that cats given stents had larger decreases in BUN and creatinine levels than cats who had surgery, both one day afterwards and at the time of discharge, though some of the stent group developed fluid in the abdomen.

The success rate is approximately 96% (though in Outcomes of ureteral surgery and ureteral stenting in cats: 119 cases (2006-2014) (2016) Wormser C, Clarke DL & Aronson LR Journal of the American Veterinary Medical Association 248(5) pp518-25 around 22% of cats blocked again), and the stent can remain in place for years. In about 5% of cases, the stent moves, but it can usually be repositioned. Other possible problems include infections and a biofilm forming on the stents, which may necessitate replacement.

Possible side effects include blood in the urine, and I have heard from a couple of people whose cats have stents that their cats seem to urinate more, which might be due to low grade inflammation from the stent. Outcomes of ureteral surgery and ureteral stenting in cats: 119 cases (2006-2014) (2016) Wormser C, Clarke DL & Aronson LR Journal of the American Veterinary Medical Association 248(5) pp518-25 found that “After surgery, signs of chronic lower urinary tract disease and chronic urinary tract infection were significantly more common among cats with than cats without stents.” I would imagine that these cats may have some degree of pain or discomfort, and some people have told me that their cats do seem to be happier when given painkillers.

The main problem with stents is their cost. One member of my support group paid US$15000 back in 2012 for a stent on one side and a SUB (see below) on the other. The stent was replaced eighteen months later at a not inconsiderable additional cost. Another member paid US$8000 for two stents in 2014. Eleven months later both stents had to be replaced at a cost of US$4700. I have heard from a couple of people that the estimates they received were a lot lower than the actual cost, so bear this in mind if you decide to go ahead.

Ureteral obstructions in dogs and cats: a review of traditional and new interventional diagnostic and therapeutic options (2011) Berent AC Journal of Veterinary Emergency and Critical Care 21(2) pp 86–103 has detailed information on the use of stents.

How I approach…ureteral obstruction in dogs and cats (2013) Berent A Veterinary Focus 23(3) pp17-25 is a more up to date report on Dr Berent’s use of stents.

Technical and clinical outcomes of ureteral stenting in cats with benign ureteral obstruction: 69 cases (2006-2010) (2014) Berent AC, Weisse CW, Todd K & Bagley DH Journal of the American Veterinary Medical Association 244(5) pp559-76 reports on 79 stents placed in 69 cats. 95% of the cats had elevated kidney values (azotaemia) before treatment and 71% of them continued to be azotaemic, though in most cases the numbers did at least improve. 27% of the cats needed a stent exchange at some point.

Subcutaneous Ureteral Bypass

A subcutaneous ureteral bypass (SUB) is a form of microsurgery that was pioneered at the Animal Medical Center in New York City. It does not aim to remove the stones unless it is easy to do so; instead, it aims to bypass the stones by providing an alternative route between the kidneys and the bladder (an artificial ureter, if you like).

Previously a stent was the first line of treatment but as SUB techniques have improved, SUBs have become more reliable and are probably a better choice if your cat is a suitable candidate (and your vet has extensive experience with them) because of the option to flush through the port, which you cannot do with a stent.

The surgery is now available at a small number of centres, including in the USA, Canada, UK, France, Switzerland, Italy and France. The American Society of Veterinary Nephrology and Urology gives locations throughout the world where these procedures are available.

Subcutaneous Ureteral Bypass: How It Works

A SUB consists of a tube within a tube surrounded by mesh that runs outside the ureter (unlike a stent, which is placed inside the ureter). Because the SUB is outside the ureter, it can be bigger than a ureter or a stent and is around 5-6mm in diameter (for comparison, a feline ureter is around 0.3mm in diameter). Therefore, although the cat may still develop kidney stones, the urine should in principle still be able to flow through because of the extra width of the device compared to a ureter.

In order for a cat to receive a SUB, the renal pelvis (the upper end of the ureter) must be dilated, so essentially your cat must have an active blockage at the time the SUB is fitted. If your cat’s renal pelvis is not dilated, you may be offered a stent instead (see above).

The cat will usually be in hospital for several days after SUB placement and will usually be fitted with a feeding tube at the same time, which will remain in place for 6-12 weeks. Some cats with SUBs are given regular sub-Qs to help avoid stone formation (not LRS, which is unsuitable because it contains calcium).

An advantage of a SUB is that it incorporates an access port in the abdomen which can be easily accessed later if necessary in order to flush out any stones that are accumulating. Initially these flushes are performed four times a year, but this may be gradually reduced to every six months. Norfolk Vet Products says “Current recommendations include flushing the SUB device prior to discharge, at 1-week post-operatively, then at 1-month, and finally every 3 months thereafter.” Your cat should not need to be an inpatient for this to be done (I am told it only takes about ten minutes). Other tests (bloodwork, blood pressure measurement and urinalysis with urine culture) should also be performed, though if your cat has CKD, you are probably having these tests run this frequently anyway.

Angell Animal Medical Center has an overview of SUBs.

Subcutaneous ureteral bypass as a treatment option for urolithiasis in cats (2021) Commons J Today’s Veterinary Nurse Winter 2022 has detailed information about SUBS in cats.

How I approach…ureteral obstruction in dogs and cats (2013) Berent A Veterinary Focus 23(3) pp17-25 is a more up to date report on Dr Berent’s use of SUBs.

Subcutaneous Ureteral Bypass: Success Rate

The success rate is good, with SUBs remaining effective in around 94% of cats over a median of two years. Predictors of outcome for cats with ureteral obstructions after interventional management using ureteral stents or a subcutaneous ureteral bypass device (2013) Horowitz C, Berent A, Weisse C, Langston C & Bagley D Journal of Feline Medicine and Surgery 15(12) pp1052-1062 found that there was no single parameter that indicated the likely outcome of a SUB or a stent but none of the cats in the study needed to have the device replaced.

Placement of subcutaneous ureteral bypasses without fluoroscopic guidance in cats with ureteral obstruction: 19 cases (2014-2016) (2017) Livet V, Pillard P & Goy-Thollot I Journal of Feline Medicine and Surgery 19(10) pp1030-1039 looked at the placement of 19 SUBs in 13 cats compared to 15 traditional surgeries performed in 11 cats. The study found that cats receiving SUBS needed a shorter period of hospitalisation than the cats receiving traditional surgery, and concludes “Ten SUB cats (76.9%) and four C cats (40%) were still alive at a median follow-up of 225 days and 260 days, respectively. Owners were completely (90%) or mostly (10%) satisfied with the SUB device placement. SUB device placement appears to be an effective and safe option for treating ureteral obstruction in cats, and this study has shown that fluoroscopic guidance is not essential in all cases.”

Use of a subcutaneous ureteral bypass device for treatment of benign ureteral obstruction in cats: 174 ureters in 134 cats (2009-2015) (2018) Berent AC, Weisse CW, Bagley H & Lamb K Journal of the American Veterinary Medical Association 253(10) pp1309-1327 discusses the use of SUBs in detail, including complications on page 1320 and success rates on page 1322 (sorry about the infuriating waving woman, but the link does give you access to the entire article). The study states that median survival time “was 827 days (range, 0.25 to 2,397 days)” and adds “No cat died during surgery or because of persistent ureteral obstruction immediately after surgery.”

Subcutaneous ureteral bypass device for treatment of iatrogenic ureteral litigation in a kitten (2015) Johnson CM, Culp WTN, Palm CA & Zacuto AC Journal of the American Veterinary Medical Association 247(8) pp924-931 reports on a 17 week old kitten who successfully received a SUB.

Subcutaneous Ureteral Bypass: Follow-Up and Possible Complications

One of the main post-operative risks is pancreatitis, so you should monitor for this.

One potential problem is infection. Risk factors for positive urine cultures in cats with subcutaneous ureteral bypass and ureteral stents (2010-2016) (2019) Kopecny L, Palm CA, Drobatz KJ, Balsa IM & Culp WTN Journal of Veterinary Internal Medicine 33(1)pp178-183 found that 25% of the cats in the study had a positive result for an infection in their urine even before discharge from hospital, and at follow up (after a median of 55 days) 25% of cats were found to have positive urine cultures. The study states “Cats that received antibiotics postoperatively were significantly less likely to have a positive urine culture compared to those that did not.” I have heard of some cats given antibiotics after a SUB, presumably for this reason.

Factors associated with positive urine cultures in cats with subcutaneous ureteral bypass system implantation (2020) Pennington CE, Halfacree Z, Colville-Hyde C & Geddes RF Journal of Feline Medicine and Surgery epub looked at cats given SUBs between 2011 and 2019. The study found that 8.5% of cats had a positive culture within a month of surgery and 23.7% within a year, and that this was more likely in cats who had a positive culture before surgery. Interestingly, the study also found that cats with a lower body temperature around the time of surgery were more likely to have an infection afterwards. See Anaesthesia for more information on the importance of maintaining body temperature during surgery.

SUBs have a tendency to form a biofilm, which may be a factor in the development of infections. Flushing the SUB may help with cases of infection or to avoid infection. T-FloLoc infection protocol (2018) Norfolk Vet Products is the recommended protocol, which lasts for thirty weeks, though the treatment frequency decreases towards the end of the period (it starts off weekly, but reduces to four weekly and towards the end to twelve weekly). The protocol claims “Successful demineralization of a SUB device was accomplished in 8/10 devices and successful eradication of recurrent urinary tract infections was successful in 3/4 patients.”

Other types of flush are also sometimes necessary. One member of my support group’s cat needed to have the SUB tubing replaced and then she had to take her cat to the vet for t-PA (tissue plasminogen activator) flushes 2-3 times a week for about a month to break up a blood clot that was presumed to be in the kidney itself. Although this was expensive (costs range from US$150-360 per flush), her cat’s kidney function did eventually return to normal.

Like a stent, sometimes a SUB has to be redone. I understand that in around 20% of cases the tubing needs to be replaced.

Ultrasound evaluation of the renal pelvis in cats with ureteral obstruction treated with a subcutaneous ureteral bypass: a retrospective study of 27 cases (2010-2015) (2017) Fages J, Dunn M, Specchi S & Pey P Journal of Feline Medicine and Surgery 20(10) pp875-883 states that “Ultrasonography appears to be an effective tool in the monitoring of cats following SUB placement.” The study found that monitoring via “ultrasound is an important tool in the detection of obstructive complications, and a renal pelvic width of >3.5 mm 3 months postoperatively is expected.”

Subcutaneous Ureteral Bypass: Cost

As with stents, one major concern with a SUB is the cost:

One member of Tanya’s CKD Support Group had this surgery performed on her cat in the USA in early 2012. She paid US$2000 for the tube. Surgery costs were an additional US$4000 – 6000.
Another member paid US$15000 that same year for a stent on one side and a SUB on the other. The stent was replaced eighteen months later at a not inconsiderable additional cost.
Another member was quoted US$5000 in 2015 for one SUB.
A fourth member was quoted US$6000-8000 but her cat had some post-surgery complications so in the end she paid around US$10000.
One member in Germany paid €2400 in 2015 for a SUB, but her cat had complications and infections, so in total over 11 months she paid around €17000 (this cost included SUB flushes).

As you can see, it is by no means uncommon for there to be complications and this can push the cost up. Subcutaneous ureteral bypass as a treatment option for urolithiasis in cats (2021) Commons J Today’s Veterinary Nurse Winter 2022 says “There may be unexpected and considerable costs related to an infection or mineralization protocol, potential revision surgery, or frequent urinalysis and urine cultures due to recurrent UTIs.”
I have also heard from a couple of people that the estimates they received were a lot lower than the actual cost, so bear this in mind if you decide to go ahead.

Other Treatments

These are more holistic treatments but as far as I know, there has been no research into these treatments in cats to date.

Chanca Piedra

Chanca piedra is a tropical plant that is sometimes used for liver problems. It has been used in Brazil to treat calcium oxalate stones. There are a number of varieties but the two varieties commonly found in chanca piedra commercial products are Phyllanthus amarus, which is from the Amazon region, and Phyllanthus niruri, which is from the Andes. WebMD has an overview of chanca piedra.

I am not aware of any studies in cats and do not know of anybody who has used chanca piedra, but there are some studies into its use in rats and humans.

In one study in rats, Effects of Orthosiphon grandiflorus, Hibiscus sabdariffa and Phyllanthus amarus extracts on risk factors for urinary calcium oxalate stones in rats (2011) Woottisin S, Hossain RZ, Yachantha C, Sriboonlue P, Ogawa Y & Saito S Journal of Urology 185(1) pp323-328, the rats were fed a diet designed to increase the presence of calcium oxalate in the kidneys. The rats in one group were then given 3.5mg of chanca piedra daily. The study found “The Hibiscus sabdariffa group showed significantly decreased serum oxalate and glycolate, and higher oxalate urinary excretion. The Phyllanthus amarus group showed significantly increased urinary citrate vs the untreated group. Histological examination revealed less CaOx crystal deposition in the kidneys of Hibiscus sabdariffa and Phyllanthus amarus treated rats than in untreated rats. Those rats also had significantly lower renal tissue calcium content than untreated rats.”

Can Phyllanthus niruri affect the efficacy of extracorporeal shock wave lithotripsy for renal stones? A randomized prospective long-term study (2006) Micali S, Sighinolfi MC, Celia A, De Stefani S, Grande M, Cicero AF & Bianchi G Journal of Urology 176(3) pp1020-1022 looked at the use of chanca piedra in 150 human patients for three months following treatment with lithotripsy. The study found that 93.5% of patients given the chanca piedra were stone-free after six months, compared to 83.3% who did not receive chanca piedra. For lower stone patients, “the stone-free rate was 93.7% in the treatment group and 70.8% in the control group.” The study concludes “Its efficacy and the absolute lack of side effects make this therapy suitable to improve overall outcomes after extracorporeal shock wave lithotripsy for lower pole stones.”

The effect of Phyllanthus niruri on urinary inhibitors of calcium oxalate crystallization and other factors associated with renal stone formation (2002) Freitas AM, Schor N & Boim MA BJU International 89(9) pp829-834 examined the use of chanca piedra in rats. It concludes “Treatment with Pn strongly inhibited the growth of the matrix calculus and reduced the number of stone satellites compared with the group receiving water. The calculi were eliminated or dissolved in some treated animals (three of 22).”

Phyllanthus niruri normalizes elevated urinary calcium levels in calcium stone forming (CSF) patients (2004) Nishiura JL, Campos AH, Boim MA, Heilberg IP & Schor N Urological Research 32(5) pp362-366 gave chanca piedra or a placebo to human patients for three months. The study concludes “we observed that P. niruri induced a significant reduction in the mean urinary calcium in hypercalciuric patients. In this short-term follow-up, no significant differences in calculi voiding and/or pain relief between the groups taking P. niruri or the placebo were detected. Our data suggest that P. niruri intake reduces urinary calcium based on the analysis of a subset of patients presenting with hypercalciuria.’

Kidney Atlas assessed a number of commercial variants of chanca piedra and found many of them were contaminated or devoid of any active ingredient. It mentions two brands that it considers to be pure.

As always, do not use any product without your vet’s approval.

Renalof

Renalof is a dietary supplement for humans made from activated couch grass (Agropyron repens). It is said to help dissolve calcium oxalate stones. It has apparently undergone trials in humans in Romania, Indonesia and Cuba.

The effectiveness of Renalof compared to Kalkurenal and placebo (2012) Kristyantoro B, Alif S, Djojodimedjo T & Budiono B Indonesian Journal of Urology 19(2) found there was a significant decrease in stone size in patients treated with Renalof.

Randomized double-blind study with Renalof in patients with calcium oxalate renal lithiasis (2012) Sánchez MCA, Villanueva VE & Vázquez RA Revista Cubana de Investigaciones Biomédicas 31(1) reports on the Cuban trial and states that “Stone size reduction was 7.7% for the Renalof group and 0% for the placebo group by the third month, whereas the stone disappearance response was 86.5% by the third month for the Renalof group… It was concluded that Renalof is an efficient product for the destruction or reduction of calcium renoureteral calculi, with no adverse effects.”

Renalof is not approved for cats, though I did hear from one lady whose vet decided to use it as a last ditch attempt to help her cat (I don’t know how she got on). As always, do not use this product without your vet’s approval.

Prognosis

Much depends upon whether the stones are static or active, how severe your cat’s case is, which treatment is used and how successful it is. Unfortunately it is difficult to stop the development of kidney stones and some of the available treatments are very expensive, but I do know of cats who have survived for years.

Management and outcome of cats with ureteral calculi: 153 cases (1984 – 2002) (2005) Kyles AE, Hardie EM, Wooden BG, Adin CA, Stone EA, Gregory CR, Mathews KG, Cowgill LD, Vaden S, Nyland TG, Ling GV. Journal of the American Veterinary Medical Association 226(6) pp937-44 discusses a large number of cases over a period of eighteen years, and states that even after successful treatment, many cats will have impaired kidney function, with elevated creatinine levels.

That study refers to cases that occurred before some of the more modern treatments were available. Rate and frequency of recurrence of uroliths after an initial ammonium urate, calcium oxalate, or struvite urolith in cats (2009) Albasan A, Osborne CA, Lulich JP, Lekcharoensuk C, Koehler LA, Ulrich LK & Swanson LL Journal of the American Veterinary Medical Association 236(12) pp1450-55 found that only 7% of cats developed calcium oxalate stones again following treatment, and the average grace period before this happened was over two years. The authors believe the actual recurrence rate may be higher than this, but it does appear that following successful treatment, the chance of recurrence may be relatively low for some cats, and this is particularly true for cats who receive newer treatments such as a stent or a SUB.

There are several members of Tanya’s CKD Support Group who have dealt with kidney stones in their cats. I will be adding some of their stories to the Success Stories page in due course (here is Mama’s story), but in the meantime feel free to join the group for information and support on the treatments available.

Prevention

Prevention is not easy, but you can take a few steps to reduce the risks. Ideally you want your cat to have a urine specific gravity below 1.30.

Follow the dietary changes outlined above.
Try to keep protein intake around 35% on a dry matter analysis basis. This is a suitable level for a CKD cat anyway.
Try to increase your cat’s water intake (see Oral Fluids). ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 advise feeding a canned food that is more than 75% water (as fed).
If your cat has hypercalcaemia (elevated calcium levels in the blood), try to get it under control, though this is not always easy.
For some cats, calcium oxalate stones may be caused by a Vitamin B6 deficiency, in which case a vitamin B supplement may help (be guided by your vet as to an appropriate brand).
Do not give your cat any supplements containing calcium.
ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 mentions using thiazide diuretics for cats with frequently recurring stones.
In some cases, potassium citrate may help to stabilise urine pH so new stones do not form. Therefore, if your cat is receiving potassium supplements, talk to your vet about giving it in this form. ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats (2016) Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW & Osborne CA Journal of Veterinary Internal Medicine 30(5) pp1564–1574 mentions giving potassium citrate to cats with persistently acidic urine. However, you should not supplement potassium unless your vet tells you to do so, because some CKD cats tend towards high potassium levels.
Have monthly x-rays or ultrasounds performed to ensure existing stones have not moved.

This page last updated: 27 June 2025

Links on this page last checked: 27 June 2025