My dog produces calcium oxalate stones: how to prevent this?

Blood Testing as diagnosis

Measuring calcium levels in the blood helps determine whether the level is too high. Elevated blood calcium can cause the kidneys to excrete more calcium into the urine, increasing the risk of stone recurrence. Blood calcium consists of total calcium and ionized calcium. Ionized calcium is the active form and is essential for determining whether calcium levels are truly too high or too low.

Treatment

Reducing the excretion of calcium and oxalate in the urine is challenging. For this reason, these stones unfortunately tend to recur more often than other types, even when the recommended steps are followed carefully. Regular monitoring remains essential.

Below we explain, in simple steps, what can be done.

1. Increase Water Intake: at least 50 ml per kg body weight per day

For all animals with urinary stones, increasing water intake is the most important measure. It is the most effective, safest and least expensive way to prevent stones. Dogs should drink at least 50 ml/kg per 24 hours.

Goal: Extra fluid dilutes the urine and reduces the chance that calcium and oxalate will crystallize again. Dogs generally drink more than cats, but even dogs often drink too little on their own. Measuring the urine specific gravity helps determine whether your dog is drinking enough: the target value is 1.020–1.025. This is measured with a refractometer. You can do this at home (available via [email protected] with instructions) or by bringing urine to your veterinarian.

Practical tips to increase water intake:

• Add water to dry food to increase moisture per meal.

• Choose water with a low calcium content, such as Spa Blue (see “Water and their calcium levels”).

• Offer wet food as an additional moisture source (optionally mixed with extra water).

• Place multiple water bowls throughout the house and garden.

• Add a small amount of cooking water from white fish or unsalted boiled chicken to encourage drinking.

• Use a drinking fountain for dogs that prefer running water.

• Measure whether your dog is drinking enough.

• Take your dog out frequently (at least 4× daily) so crystals have less time to clump together.

2. Choose the Right Diet: low calcium, low sodium

It is important to choose a diet that matches the type of stone and to follow it strictly. There is no 100% guarantee that stones will never recur.

Calcium oxalate stones cannot be dissolved with diet. Prevention is therefore the most important goal. The diet essentially functions as a form of medication. The crystal type indicates what needs attention:

• Calcium oxalate dihydrate (COD): avoid high sodium intake, as calcium follows sodium into the urine via the kidney tubules.

• Calcium oxalate monohydrate (COM): minimize oxalate precursors in the diet and maintain a normal urine pH.

Goals of the diet:

• • Slightly increase urine pH (less acidic).

  • Reduce calcium and oxalate intake.

  • Keep sodium and protein balanced.

  • Increase urine volume.

Practical tips for diet success:

• • • Divide meals into 3–4 portions per day to keep urine pH stable.

    • Avoid snacks labeled “Urinary,” as they often acidify the urine (e.g., cranberry, citric acid).

    • Avoid table scraps high in calcium, sodium or oxalate (see “Food and their levels”).

    • Do not create a homemade diet without veterinary or nutritionist guidance.

    • Keep your dog at a healthy weight, as excess weight promotes stone formation.

It is extremely important that your dog receives nothing other than the prescribed diet. The food is the key to success.

3. Follow‑up and Monitoring

Regular monitoring is essential to determine whether the diet is having the desired effect.

Within 2 weeks after starting the diet

• Check urine specific gravity 🏋️‍♀️ — must be below 1.025.

• Check urine pH 🍋 — target pH for calcium oxalate is 7.5. This can be done at the vet or at home using pH paper (available via [email protected] or at pharmacies).

Four weeks after starting the diet

• Recheck urine specific gravity.

• Recheck urine pH (target 7.0–7.5).

• Check urine sediment for calcium oxalate crystals.

• Perform an ultrasound of the bladder to check for stones.

• If kidney stones were previously present, take an abdominal X‑ray (same side each time) to monitor growth or stability.

Three‑monthly checks

If urine pH, specific gravity and sediment remain stable, you can switch to 3‑monthly checks. Bladder ultrasound is the most important test, as it detects stones early.

If all measures are insufficient

• If the pH remains too acidic (6.5 or lower), potassium citrate may be added (see “Potassium citrate supplementation in dogs”).

If stones recur:

• Small stones (that can pass through the urethra) may be flushed out by increasing water intake and frequent urination.

• Larger stones may require:

  • Catheterization and flushing

  • Urethroscopy to retrieve stones

  • Endoscopic removal via the bladder

  • Surgical removal (less preferred due to invasiveness)

Before adjusting treatment, it is important to evaluate whether dietary improvements are still possible. This may require guidance from a nutrition specialist and reviewing all previous diets, blood calcium levels and urine calcium 

levels.

If diet alone cannot improve the situation, medication such as hydrochlorothiazide may be used to reduce calcium excretion by the kidneys (see “Medication in urology”).

At Specialist Bouvien, we focus on guiding animals with urinary stone formation.

This information is based on scientific literature, the Minnesota Urolith Center (USA), and daily clinical experience at Specialist Bouvien.