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Bladder stones in dogs: urine tests, crystals and X-rays

Bladder stones (uroliths) are hard mineral lumps that form in the urinary tract. The urine test gives clues, but crystals in a urine sample are not the same as stones. Imaging finds the stones, and analysis of a removed stone tells which type it is.

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

The essentials

The two main stone types in dogs are calcium oxalate and struvite. Struvite stones are often linked to a urinary infection and can often be dissolved with medical treatment; calcium oxalate stones cannot. Crystals can appear in the urine of healthy dogs or form in a stored sample, so urine is best examined within 60 minutes. A urine culture, X-rays or ultrasound, and analysis of the stone guide the plan.

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The main types of bladder stones

In a study of 10,444 dog stones analysed at UC Davis, calcium oxalate made up 47.0% and struvite 43.6%. Cystine was rarer but rising, from 1.4% of stones in 2006 to 8.7% in 2018 [2]. The type matters, because it changes the urine findings, the tests and whether the stone can be dissolved [1].

Stone types in dogs, from a large US laboratory series and the ACVIM consensus.
Stone typeWhat favours itWho is most at risk
StruviteNeutral to alkaline urine. A urinary infection with urease-producing bacteria raises the urine pH [1, 3].Mostly females (81.1%) and young dogs (62.0% under 4 years) [2].
Calcium oxalateMainly high calcium in the urine [1]. Its crystals form at any urine pH [3].Mostly males (75.2%) and older dogs (79.5% aged 7 or more) [2]. Miniature Schnauzer, Lhasa Apso, Yorkshire Terrier, Bichon Frise, Shih Tzu, Poodles, Maltese, Pomeranian; overweight dogs [2, 5].
UrateA gene variant (SLC2A9) and liver shunts [1].Dalmatians (odds ratio 85.5) and English Bulldogs [2].
CystineAcidic urine favours cystine crystals [3]. Some forms depend on male hormones [1].Almost only males (98.2%), most of them not neutered (70.3%) [2].

Crystals are not stones

Crystals can be seen in the urine of clinically healthy animals [3]. On their own, they do not mean that your dog has stones.

Crystals can also form in the sample after collection. In one study, crystals formed in the test tube in 11 of 39 urine samples (28%). Refrigeration increased their number and size, and longer storage and colder temperatures increased calcium oxalate crystals [4]. Calcium oxalate crystals “can also be an artifact of storage” [3]. The authors recommend examining urine within 60 minutes, and checking crystals found in stored urine on a fresh sample [4]. See urinalysis in dogs and cats.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
pH Urine pH8.0–Set by each lab–
  1. Abbreviation pH: how acidic or alkaline the urine is, read on the dipstick.
  2. Result 8.0 in this illustrative line: an alkaline urine. A urinary infection with urease-producing bacteria can raise the pH [3].
  3. Unit pH has no unit.
  4. Laboratory interval Each laboratory sets its own interval. The pH of a sample can also change while it stands [3].
  5. Flag An alkaline pH favours struvite crystals [3], but pH monitoring does not replace a urine culture to look for infection [1].

What urine culture and blood tests add

  • Urine culture: infection-induced struvite is the most common struvite stone in dogs. Urine (or the stone) should be cultured before antibiotics are started [1].
  • Urinalysis alone is not enough: routine urinalysis is an insensitive marker of urinary infection, and the sediment and pH are not substitutes for a culture [1]. See urinary tract infections in dogs and cats.
  • Bacteria in the stone: in the UC Davis series, 41.8% of cultured struvite stones grew bacteria [2].
  • Follow-up cultures: the ACVIM consensus suggests repeating the culture monthly for 2–3 months [1].
  • Blood calcium: with calcium oxalate stones, vets check ionized and total calcium in the blood [1]. See high calcium in dogs and cats.
  • Liver tests: urate stones are linked to liver shunts as well as to a gene variant [1], so your vet may add liver tests. See liver shunt in dogs.

X-rays, ultrasound and stone analysis

  • Plain X-rays missed bladder stones in 2–27% of cases, depending on the stone type, in a bladder model study. Ultrasound at 7.5 MHz performed about as well as double-contrast X-ray studies, but worse at lower frequencies [6].
  • Urate and cystine were long described as invisible on X-rays, yet 85% of urate and 92% of cystine bladder stones were visible on plain X-rays in a 2024 study [7].
  • What the X-ray suggests: in 202 dogs at the Alfort veterinary school (France), struvite stones were larger (cut-off 11 mm or more), calcium oxalate stones were very dense and often came with kidney stones, and cystine stones were less dense [8]. In an older series, about 94% of bladder stones in females were struvite, and stones over 10 mm were more than 92% likely to be struvite [9].
  • Stone analysis: only analysis of a removed or passed stone gives its exact type. Laboratories use optical crystallography, infrared spectroscopy and X-ray diffraction [2].

Treatment and recurrence in general terms

According to the ACVIM consensus, struvite stones should be dissolved with medical treatment, unless there is a blockage, a large single stone filling the bladder, treatment that cannot be given, or an infection that cannot be controlled [1]. Sterile struvite bladder stones usually dissolve in less than 2–5 weeks [1]. In a small study of infection-induced struvite, stones dissolved in 8 of 11 dogs, after a median of 2 months; the stones that did not dissolve contained calcium oxalate [10]. Calcium oxalate stones cannot be dissolved with medical treatment [1]; they are removed, and your vet will explain the options.

Calcium oxalate and urate stones have a high recurrence rate [1]. Miniature Schnauzers had 3 times the risk of calcium oxalate recurrence in one study [12]. Stones that form around stitch material were 0.6% of all dog bladder stones but 9.4% of recurrent ones [11]. No reliable overall recurrence rate is available, so follow-up urine tests and imaging are planned with your vet.

Related articles

Urinalysis in dogs and cats

Specific gravity, dipstick, crystals and sediment.

Read the article

Urinary tract infections in dogs and cats

Why a urine culture is needed.

Read the article

En français : calculs urinaires du chien.

Questions to ask your veterinarian

  1. Were the crystals seen in fresh urine, and do they matter here?
  2. Has a urine culture been done, ideally before antibiotics?
  3. What type of stone is most likely, and will the stone be analysed?
  4. Can this stone be dissolved, or does it need to be removed?
  5. Which urine tests and imaging should we repeat, and when?
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Frequently asked questions

What is the main cause of bladder stones in dogs?

It depends on the stone type. The most common struvite stones in dogs are caused by a urinary infection with urease-producing bacteria. Calcium oxalate stones are driven mainly by high calcium in the urine. Urate stones are linked to a gene variant and to liver shunts [1].

Can dogs survive bladder stones?

Yes, most can be managed. Struvite stones can often be dissolved with medical treatment, and other stones can be removed [1]. A blockage of the urethra, however, is an emergency.

What foods dissolve bladder stones in dogs?

Only some stones can be dissolved. Struvite stones can often be dissolved with a medical plan prescribed by your vet; calcium oxalate stones cannot [1]. Do not change your dog’s food without knowing the stone type.

How long can a dog go with bladder stones?

There is no safe waiting time. A stone can move and block the urethra, especially in males. A dog that strains without passing urine needs a vet immediately.

Are crystals in my dog’s urine the same as bladder stones?

No. Healthy dogs can have crystals, and crystals can form in a sample that waits or is refrigerated. Urine is best examined within 60 minutes [3, 4].

Sources

  1. Lulich JP et al. ACVIM Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats. J Vet Intern Med. 2016;30(5):1564-1574. doi.org/10.1111/jvim.14559
  2. Kopecny L et al. Urolithiasis in dogs: evaluation of trends in urolith composition and risk factors (2006-2018). J Vet Intern Med. 2021;35(3):1406-1415. doi.org/10.1111/jvim.16114
  3. eClinPath, Cornell University College of Veterinary Medicine. Crystals. eclinpath.com/urinalysis/crystals
  4. Albasan H et al. Effects of storage time and temperature on pH, specific gravity, and crystal formation in urine samples from dogs and cats. J Am Vet Med Assoc. 2003;222(2):176-179. doi.org/10.2460/javma.2003.222.176
  5. Lekcharoensuk C et al. Patient and environmental factors associated with calcium oxalate urolithiasis in dogs. J Am Vet Med Assoc. 2000;217(4):515-519. doi.org/10.2460/javma.2000.217.515
  6. Weichselbaum RC et al. Urocystolith detection: comparison of survey, contrast radiographic and ultrasonographic techniques in an in vitro bladder phantom. Vet Radiol Ultrasound. 1999;40(4):386-400. doi.org/10.1111/j.1740-8261.1999.tb02131.x
  7. Andrews C et al. Cystine and urate cystoliths in dogs are frequently visible on radiographs. J Am Vet Med Assoc. 2024;262(10):1338-1342. doi.org/10.2460/javma.24.05.0302
  8. Pulido Vega D et al. In vivo radiographic characteristics of calcium oxalate, struvite, and cystine lower urinary tract uroliths in dogs. J Vet Intern Med. 2025;39(6):e70252. doi.org/10.1111/jvim.70252
  9. Weichselbaum RC et al. Evaluation of the morphologic characteristics and prevalence of canine urocystoliths from a regional urolith center. Am J Vet Res. 1998;59(4):379-387. pubmed.ncbi.nlm.nih.gov/9563616
  10. Harris ASM et al. d,l-Methionine in combination with amoxicillin-clavulanic acid successfully dissolves spontaneously occurring infection-induced struvite urocystoliths in dogs: a pilot study. J Am Vet Med Assoc. 2023;261(8):1152-1159. doi.org/10.2460/javma.23.02.0063
  11. Appel SL et al. Evaluation of risk factors associated with suture-nidus cystoliths in dogs and cats: 176 cases (1999-2006). J Am Vet Med Assoc. 2008;233(12):1889-1895. doi.org/10.2460/javma.233.12.1889
  12. Allen HS et al. Associations of diet and breed with recurrence of calcium oxalate cystic calculi in dogs. J Am Vet Med Assoc. 2015;246(10):1098-1103. doi.org/10.2460/javma.246.10.1098

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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