Urinary stones — dissolve it or remove it?
Your vet points at the bladder on the X-ray. "There's a stone." On the way home, every search gives two answers that collide: "a prescription diet will dissolve it" and "it has to come out". Both are right — depending on what the stone is made of.
Bladder stones in cats are almost always one of two kinds. Of 28,714 feline stones analysed by the Minnesota Urolith Center (MUC) in 2025, 45% were struvite and 42% calcium oxalate; 7% were urate. One dissolves with diet; the other dissolves with nothing. This article starts at that fork and works through how to dissolve, when to remove, and the numbers that keep stones from coming back.
| Who | Decides what |
|---|---|
| You, at home | Water and wet-food share, cutting out treats and mixed-in foods, watching urination, keeping recheck dates |
| You and your vet | Whether to try dissolving and for how long, the prevention diet, recheck intervals |
| Your vet | How a stone is removed and the anaesthesia, prescriptions |
The numbers in this article belong to the middle row: baselines to bring when you decide together with your vet.
1. "Crystals" on a urine report are not yet a stone
Crystals on a urinalysis are tiny particles seen under the microscope; a stone is what shows up on X-ray or ultrasound. A cat can have crystals and no stone, or a stone and no crystals.
Crystals also form during testing. In 41 healthy cats, 24% had crystals in urine examined straight away, but among cats eating some dry food, 92% showed crystals in at least one stored sample; cats eating only wet food showed none (Sturgess 2001). Refrigeration and time increase crystals, so the standard is to examine urine within 60 minutes at room temperature (Albasan 2003, iCatCare 2025).
① Check that the sample was examined within 60 minutes. If it was collected at home or refrigerated, repeat it.
② Struvite crystals in a cat without signs may not need treatment on their own (Merck).
③ Meanwhile, the one thing to do is increase water intake (section 5).
2. Which stone is it — the two compared
| Struvite | Calcium oxalate | |
|---|---|---|
| Share | 45% | 42% |
| Urine it forms in | Alkaline side (pH 6.5 and above) | Acidic side; calcium-rich urine |
| Cats at higher risk | — | Middle-aged and older (mean about 7.5 years), neutered; Ragdoll, British Shorthair, Himalayan, Scottish Fold, Persian |
| On X-ray | Faint to moderate once over 3 mm | Dense; usually 1–4 mm |
| Dissolves with diet? | Yes — study means 13–27 days | No — not with diet, not with medicine |
| Bacteria involved? | Mostly sterile (culture-positive 10.9%) | — |
| First choice | Dissolution diet | Remove or watch, depending on signs and size |
| Prevention | Dilute urine + pH below 6.5 | Dilute urine + avoid acidification + look for a calcium cause |
| Recurrence (minimum estimate) | 2.7%, mean 29 months later | 7.1%, mean 25 months later |
Sources: share MUC 2025; risk factors Lekcharoensuk 2000; X-ray iCatCare 2025; dissolution time Lulich 2013; sterility Kopecny 2021; recurrence Albasan 2009 (it counts only stones re-submitted to the lab, so real rates are higher).
Urate (7%) barely shows on X-ray and is found with ultrasound. The composition can only be confirmed by analysing a removed stone; until then it is estimated from its X-ray appearance, urine pH and the cat's age.
3. Struvite — two to four weeks to dissolve
Unlike in dogs, struvite in cats usually forms without infection: of 503 cultured struvite-containing stones, only 10.9% grew bacteria (Kopecny 2021). So treatment centres not on antibiotics but on a dissolution diet that shifts urine to the dissolving side, and the ACVIM consensus (2016) recommends dissolving bladder struvite first.
How long does it take? In a randomised trial of 37 cats, the 32 whose stones fully dissolved took a mean of 13 or 27 days, depending on the food (Lulich 2013). Another study found a median of 18 days (range 10–55) (Houston 2011). In both, the stones that never dissolved turned out not to be struvite (urate, calcium oxalate, calcium phosphate).
· Feed the dissolution diet only. Treats and other foods undo the formula that pushes urine into the dissolving range. Tell your vet about any food you use to give pills.
· X-ray after 2–3 weeks to check the size (iCatCare 2025, MUC).
· If it's smaller, continue and re-image in 2–4 weeks (MUC).
· Some experts advise feeding it for about a month more after the stones disappear from the X-ray, for fragments too small to see (expert review, Grauer 2015).
· No change in size at 2–3 weeks → it may not be struvite, or other food may be getting in. Don't drag the diet out for months; discuss re-estimating the type and removal.
· Barely eating the diet for more than a day → don't let the cat go hungry. Other formats (dry ↔ wet) exist for the same purpose.
· A male straining without passing urine → urethral blockage during dissolution has not been reported (ACVIM 2016), but whatever the cause, it's an emergency (chapter 02).
Why no mixing? A dissolution diet is designed to bring the urine's struvite relative supersaturation (RSS) below 1, the dissolving zone. In the "metastable" zone above 1, fewer new crystals form, but existing stones won't dissolve and can even grow (US FDA Guidance #284). Other foods can push urine back into that zone.
4. Calcium oxalate — remove or watch
Calcium oxalate does not dissolve with diet or medicine (ACVIM 2016, iCatCare 2025). The options are to remove it or to watch it. ACVIM divides it like this.
| Situation | ACVIM recommendation |
|---|---|
| Causing signs such as blood in the urine or frequent urination | Remove — by the least invasive method available |
| No signs, but close to the width of the urethra | Remove — it could block on the way out |
| No signs, and unlikely to block | Watch — periodic imaging + owner education |
How it's removed depends on the stone's size and the cat's sex.
| Method | How | Good to know |
|---|---|---|
| Voiding urohydropropulsion (VUH) | Under anaesthesia, the bladder is expressed so stones flush out with urine | Only stones smaller than the urethra — about 1 mm in males, up to about 5 mm in females (review). No incision |
| Cystoscopic basket | Grabbed with an endoscope | Mainly females; the male urethra is too narrow for most scopes (ACVIM) |
| Percutaneous cystolithotomy (PCCL) | Small incision + endoscope | Named the procedure of choice in males (Bartges 2016). In 28 cats, poor outcomes 21% vs 71% with open surgery (Buote 2022) |
| Cystotomy (open surgery) | The abdomen is opened | Available at almost any clinic. Checking for leftover stones is essential |
· Image right after removal to confirm nothing was left behind. Experienced surgeons have been reported to leave stones in about 1 in 5 cats (cited by MUC, from a 1993 conference abstract), and leftovers are a common cause of "rapid recurrence".
· Send the stone for analysis. The Minnesota Urolith Center analyses stones free of charge (the clinic pays for shipping); outside the US, submissions go through the regional Hill's office, and some local veterinary labs also offer stone analysis.
· If it's calcium oxalate, measure ionised calcium. In 434 feline samples, total and ionised calcium disagreed 40% of the time, and 64% of samples with high ionised calcium had a normal total calcium (Schenck 2010).
5. Keeping them away — three numbers
One prevention works for both stones: dilute urine. Then pH, then the recheck schedule.
| Number | Target | Source |
|---|---|---|
| Urine specific gravity (USG) | Below 1.030 | ACVIM 2016 |
| Urine pH — after struvite | Below 6.5, but not below 6.2 for long | ACVIM 2016, MUC |
| Urine pH — after calcium oxalate | 6.5–7.5 (avoid acidification below 6.5) | ACVIM 2016, MUC |
| Rechecks — after calcium oxalate | Urinalysis monthly until on target, then every 3–6 months Imaging every 6–12 months | MUC |
The numbers have reasons. Cats on the highest-moisture diets (74–81%) had about a third of the calcium oxalate risk of cats on the driest diets (OR 0.38), and diets producing a urine pH of 5.99–6.15 carried about three times the risk of diets producing pH 6.5–6.9 (Lekcharoensuk 2001 — the diets studied date from the 1980s–90s and may differ from today's products). Being overweight (OR 2.8) and living strictly indoors (OR 3.0) were also linked to risk.
Worked example — same 200 kcal, different water
A cat eating 200 kcal a day of dry food (about 380 kcal per 100 g, 10% moisture) eats about 53 g and gets about 5 ml of water from it. The same 200 kcal of wet food (about 95 kcal per 100 g, 80% moisture) is about 210 g and brings about 170 ml. That's a gap a water bowl rarely closes.
Adding water to dry food works too. When the same food was brought to 73% moisture, total daily water rose from 103 to 145 ml (about 40% more) and calcium oxalate supersaturation halved, from 2.29 to 1.14 (Buckley 2011, 6 cats). Water fountains, on the other hand, didn't meaningfully increase intake in three controlled studies (Grant 2010 and others). Use one if your cat likes it, but put your hopes in wet food and added water.
· Run the calculation above with the kcal and moisture % on your food's label. If you log meals in the app, the Hydration line in Daily care adds up food moisture, drinking and fluids separately.
· The answer to "is it enough water?" is the recheck USG, not the water bowl. Below 1.030 is the right side.
· Recheck USG 1.030 or higher → raise the wet-food share a step, or add water to every meal.
· A calcium oxalate cat's pH staying below 6.5 → first check the food and supplements for acidifiers (methionine, cranberry and the like).
· Weight going up → overweight is a risk factor. Lose it slowly, within 1–2% of body weight a week.
6. Does our food fit the targets — checking in the app
The Urinary tab on a product page shows magnesium, phosphorus and calcium per 1,000 kcal, moisture, the urine pH direction estimated from the ingredients, and oxalate-containing ingredients on one screen. Label percentages can't be compared across products because of water, so compare per 1,000 kcal.
· Moisture — exactly the calculation in section 5. Wetter is better.
· Magnesium — a struvite indicator. If it shows a caution, rank the food lower for a cat with a struvite history.
· Estimated urine pH — shown from the struvite point of view. "Helps acidify" is a plus for a struvite cat, but not for a calcium oxalate cat.
7. Where opinions differ
① After struvite dissolves — a prescription diet for life?
Why they differ — those worried about recurrence keep recommending a prevention diet; others point out that recurrence is uncommon. In the urolith center's data, 2.7% of struvite cases came back within five years (Albasan 2009, a minimum estimate).
Our view — with no recurrence and no history of male urethral blockage, the yardstick is "a diet that keeps the target numbers" rather than "a prescription diet for life". If a high-moisture diet keeps urine pH below 6.5, an ordinary wet food is an option. After a second recurrence, or with a blockage history, we side with a prevention diet.
How to check in your cat — after switching, test fresh urine (examined within 60 minutes) at one and three months for USG, pH and crystals. If it's off target, switch back.
② A "urinary diet" for a calcium oxalate cat
Why they differ — many urinary diets say they target both struvite and calcium oxalate. Those claims rest on urine relative supersaturation (RSS) testing, and ACVIM notes that RSS may not correlate well with actual calcium oxalate formation. Meanwhile, in epidemiological data, diets producing a urine pH around 6.0 roughly tripled calcium oxalate risk (Lekcharoensuk 2001).
Our view — after calcium oxalate, go by the actual urine pH, not the product name. If the cat also has kidney disease, the direction is a renal diet, not a urinary one (→ CKD Bible, kidney stones).
How to check in your cat — if fresh-urine pH stays below 6.5 a month after starting the food, treat it as not right for this cat.
③ Drugs to reduce recurrence — potassium citrate and hydrochlorothiazide
Why they differ — the evidence for both leans on dogs or healthy cats. Hydrochlorothiazide lowered calcium oxalate supersaturation by 65% in healthy cats but did not reduce urinary calcium itself (Hezel 2007), and potassium citrate has no controlled studies in cats.
Our view — water and diet first; drugs are the second line. We see them as options to discuss for calcium oxalate that recurs within a year (a thiazide, when blood calcium is normal — MUC) or for urine that stays acidic despite diet changes (potassium citrate — ACVIM).
How to check in your cat — measure urine pH, USG and electrolytes under the same conditions before and after starting, and compare.
8. From our records — Seungri's kidney stone
Seungri, the 16-year-old cat of the person who built this app, has stage 3 kidney disease, and in July 2026 a stone was found inside his kidney. A kidney stone can't be analysed without removing it, so based on imaging it is presumed to be calcium oxalate: 76% of feline kidney and ureteral stones were calcium oxalate (MUC 2022–23 lab data; ACVIM puts it above 90%). It sits in the kidney, not the bladder, but the conditions that form calcium oxalate are the same wherever it sits. Reading his test history backwards, the clues show.
| Date | Record | Reading |
|---|---|---|
| 2026-02 | Urine pH 6.0 · USG 1.016 | Urine already dilute from kidney disease; pH below 6.5 |
| 2026-05-23 | Urine pH 7.5 | After switching his fluids to an acetate-based solution |
| 2026-05-26 | Total calcium 11.3 mg/dL (high) | Two months before the stone was found |
| 2026-06-29 | Urine pH 6.5 · total calcium 10.4 | |
| 2026-07-25 | Kidney stone found (presumed calcium oxalate) | |
| 2026-09-08 | Urine pH 5.5 · USG 1.013 · total calcium 10.3 | Back toward acidic |
Three things we learned.
- Dilute urine alone may not be enough. His USG was 1.013–1.016, far more dilute than the target, and a stone still formed. Water is necessary, but the calcium and pH side needs looking at too.
- Urine pH moves. Changing the fluid type took it from 6.0 to 7.5, and four months later it was back at 5.5. Don't conclude from one pH reading; record it at every recheck.
- We haven't measured his ionised calcium yet. It was on the request list and got missed. We plan to check ionised calcium, PTH and vitamin D at the next test — by our own section 4, we're not fully there yet either.
9. Numbers to bring home from the clinic
Bringing home numbers comes before a list of questions. With these numbers you can match them against the tables above, and what to ask narrows down on its own.
| Bring home | Match against |
|---|---|
| Stone location, count, size of the largest (mm), whether it shows on X-ray | Section 2 comparison · section 4 removal criteria |
| Estimated composition and what it's based on | Dissolve (section 3) or remove (section 4) |
| USG, pH, crystals + how the urine was collected and how long until it was examined | Section 1 (60 minutes) · section 5 targets |
| Total calcium; ionised calcium if calcium oxalate | Section 4, calcium cause |
| If removed: stone analysis and imaging right after surgery | Section 4 · recurrence plan |
| Next urinalysis and imaging dates | Section 5 recheck schedule |
Once you have the numbers, the questions that remain look like this: "If it's unchanged on the 2–3 week X-ray, what's next?" "Will you image right after removal?" "Can we check ionised calcium too?"
10. Read next
- 02 Urinary obstruction — when a male cat is straining
- 07 Choosing a therapeutic diet — dissolution vs prevention diets
- 08 Water and litter box records — how to measure water
- CKD Bible: Do kidney stones and CKD need different care? — kidney and ureteral stones, calcium control
📌 Half of stone care is knowing what the stone is; the other half is keeping USG below 1.030.