What Happens When Your Cat Has Calcium Oxalate Crystals?

If your cat’s vet just mentioned calcium oxalate crystals or bladder stones, it’s completely normal to feel overwhelmed. These tiny mineral deposits can cause real discomfort for your cat, and how you treat them is different from other urinary conditions, so it’s worth understanding what you’re actually dealing with.

Here’s what you need to know: calcium oxalate crystals in cats are hard mineral formations that develop in the urinary tract. Unlike some other types of crystals, they can’t be dissolved with diet changes alone. But with the right vet care and a solid home monitoring plan, most cats do well long-term.

What are calcium oxalate crystals in cats, and what causes them?

Think of calcium oxalate crystals as tiny, sharp mineral particles that form in your cat’s urine. On their own they’re microscopic, but given the right conditions, they can clump together and harden into bladder stones. That’s when they start causing real problems.

It’s worth knowing how they differ from struvite, the other common crystal type in cats. Struvite stones can often be dissolved with a prescription diet, which makes them easier to manage. Calcium oxalate stones can’t be dissolved. Once they’ve formed and are causing your cat discomfort, they need to be physically removed. That’s what makes catching them early, and preventing recurrence, so important.

As for what causes them, it’s rarely just one thing. A few factors that commonly contribute:

• Too much calcium in the blood (hypercalcemia): When the kidneys can’t keep up with excess calcium, it spills into the urine and sets the stage for crystals to form.
• Acidic urine: Crystals are more likely to develop when urine pH drops below 6.5. Diet and hydration both play a role here.
• Not enough water: Cats that don’t drink much produce concentrated urine, which means more minerals packed into every drop and a higher chance of crystallization.
• A diet high in oxalate: Certain foods naturally contain more oxalate, which can increase how much ends up in your cat’s urine.
• Weight: Overweight cats have a higher overall risk for urinary issues, including stone formation.
• Age and breed: Cats between 5 and 14 are most commonly affected, and Burmese, Himalayan, and Persian cats are genetically more prone to this condition.

Symptoms of calcium oxalate crystals in cats

Your cat can’t tell you something’s wrong, so knowing what to look for makes all the difference. Whether your cat has crystals in their urine or fully formed bladder stones, the signs tend to look similar from the outside. Here’s what to watch for:

• Straining to urinate or sitting in the litter box for a long time with little output
• Blood in the urine (urine looks pink, red, or brownish)
• Urinating in unusual spots outside the litter box
• Frequent trips to the litter box, often producing only a small amount
• Crying out or showing discomfort while urinating
• Over-grooming or licking the lower belly or genitals
• Lethargy, reduced appetite, or seeming generally off

If your cat is straining but producing no urine at all, that’s a urinary blockage and it’s a medical emergency. Get to a vet immediately, this one really can’t wait.

How vets diagnose and remove calcium oxalate stones

Diagnosis

Your vet will usually start with a urinalysis, which checks your cat’s urine for crystals, blood, pH, and signs of infection, and bloodwork to look at calcium levels and kidney function. From there, X-rays or an ultrasound will show whether stones have formed and where they’re sitting. If stones are removed, your vet will send them to a lab to confirm the exact mineral type, which helps shape your cat’s prevention plan going forward.

Removal options

Because these stones can’t be dissolved, they need to come out. Your vet will recommend the best approach based on your cat’s stone size, location, and overall health. The three main options are:

• Cystotomy: The most common approach for larger stones. Your vet opens the bladder to remove them directly. It has a high success rate and is well-tolerated by most cats.
• Cystoscopy: A less invasive option for smaller stones, where a tiny camera and tool are passed through the urethra to retrieve them without surgery. More commonly used in female cats due to anatomy.
• Voiding urohydropropulsion: A non-surgical technique where fluid pressure is used to flush small stones out through the urethra. Again, more feasible in female cats, and only works for smaller stones.

Whatever route your vet recommends, the goal is the same: get your cat comfortable and set them up for a solid prevention plan afterward.

Preventing and monitoring calcium oxalate stones in cats

Once your cat has had calcium oxalate stones, prevention becomes a permanent part of their care. The recurrence rate is real, but the good news is that the tools available to you are manageable, and a lot of it comes down to things you can do at home every day.

Prescription diet

Your vet will likely recommend a prescription urinary diet designed to keep urine pH in the target range of 6.8 to 7.5 and reduce the minerals that lead to crystal formation. Commonly prescribed options include Hill’s, Royal Canin, and Purina Pro Plan. Don’t swap these out for an over-the-counter urinary food without checking with your vet first. The formulations are meaningfully different, and getting it right matters for long-term prevention.

Hydration

More water in means more dilute urine, which means fewer crystals. Wet food is one of the easiest ways to increase your cat’s daily water intake without much effort on their part. A cat water fountain can also help, since many cats prefer moving water and drink more when it’s available. Your vet may even suggest adding a splash of water directly to your cat’s food.

Potassium citrate

For some cats, your vet may prescribe potassium citrate, a supplement that helps raise urine pH and reduces crystallization. It’s not something every cat needs, but it’s a useful option when diet alone isn’t quite getting urine pH into the right range.

Keeping an eye on things at home

Between vet visits, a little daily attention goes a long way. Cats need roughly 50-60ml of water per kilogram of body weight per day from all sources. If your cat eats wet food, a good chunk of that is already covered. Beyond hydration, a quick daily litter box check is one of the simplest ways to catch a problem early. You’re looking for normal clump size, no blood or discoloration, and a consistent urination frequency of around 2 to 4 times a day. A quick note in your phone once a week, just urination frequency and anything unusual, gives your vet genuinely useful data at follow-up appointments.

Follow-up urinalyses are typically recommended every 3 to 6 months after a diagnosis. These routine checks are how your vet catches crystal recurrence before stones have a chance to form again.

When to call your vet

If you notice any of the following, don’t wait for the next scheduled appointment:

• Straining with little or no urine output
• Any blood visible in the urine
• Your cat stops using the litter box entirely
• Crying out during urination
• Lethargy or loss of appetite alongside any urinary changes
• No urination at all

Does pet insurance cover calcium oxalate stones in cats?

Treating calcium oxalate bladder stones isn’t cheap. Between urinalyses, imaging, bloodwork, surgery (cystotomy), and follow-up monitoring, costs can add up quickly. That’s where Lemonade Pet insurance can help.

Lemonade’s illness coverage can reimburse eligible diagnostics, surgical procedures like cystotomy, and medications when they’re related to a covered condition. The key detail: coverage applies to new conditions that develop after enrollment. If your cat has already been diagnosed or shown symptoms, that condition would be considered pre-existing and wouldn’t be covered.

Before we go

A calcium oxalate diagnosis is genuinely stressful, especially when you learn that diet alone won’t dissolve the stones. But your cat has a real path forward: the right removal procedure, a prescription diet tailored to prevention, better hydration, and consistent monitoring at home. The daily check-ins feel small, but they’re how you catch a recurrence early, before it becomes a bigger problem.

Work closely with your vet, stick to the follow-up schedule, and don’t wait to get a quote on pet insurance if your cat isn’t already covered. The earlier you enroll, the more options you’ll have when it matters most.

Frequently Asked Questions

A few quick words, because we <3 our lawyers: This post is general in nature, and any statement in it doesn’t alter the terms, conditions, exclusions, or limitations of the policies issued, which differ according to your state of residence. You’re encouraged to discuss your specific circumstances with your own professional advisors. The purpose of this post is merely to provide you with info and insights you can use to make such discussions more productive! Naturally, all comments by, or references to, third parties represent their own views, and Lemonade assumes no responsibility for them. Coverage may not be available in all states. Please note that statements about coverages, policy management, claims processes, Giveback, and customer support apply to policies underwritten by Lemonade Insurance Company or Metromile Insurance Company, a Lemonade company, sold by Lemonade Insurance Agency, LLC.  The statements do not apply to policies underwritten by other carriers.