Crystalluria (the presence of urine crystals) is a relatively common condition in cats. It forms part of a variety of issues cats can experience with their lower urinary tract, grouped under the blanket term ‘feline lower urinary tract disease’ (FLUTD). The lower urinary tract means the bladder and urethra (the tube that carries urine from the bladder out of the body). Let’s take a look at what urine crystals actually are, and why cats get them.

What are urine crystals? 

Urine crystals are made of minerals that would usually dissolve in urine. Urine crystals form when these minerals are oversaturated, don’t dissolve and stick together.  

Two common types of crystals in cats are struvite (made of magnesium, ammonium and phosphate) and calcium oxalate. 

The crystals that form are tiny, so you won’t be able to see them. They can only be seen under a microscope. 

What causes urine crystals? 

There are many factors that predispose to urinary crystals: 

  • Altered urine pH 
  • Concentration of the urine 
  • Diet (un-balanced or high mineral diets) 
  • Concentration of minerals in the urine 
  • Some toxins 
  • Stress (so holding their urine too long) 
  • High levels of calcium in the blood (hypercalcaemia) 

Some breeds are more prone to urinary crystals, such as Persian cats, and males are at greater risk.  

Crystalluria can increase the likelihood of your cat developing bladder or urethral stones, which are uncomfortable, and can be life threatening if they cause a blockage. 

Urine crystals can also form in urine after your cat has passed it, over time. These are not clinically significant, as they only form once the urine is outside of the body. However, it’s important to be aware of this, since crystals can form in as little as a couple of hours. So, if your vet requests a urine sample for your cat, it’s important that you take a fresh sample.  

What are the symptoms of urine crystals in cats? 

The crystals themselves do not cause any symptoms. However, they often form part of other urinary tract issues (FLUTD), such as bladder stones or feline idiopathic cystitis (FIC). If this is the case, symptoms of FLUTD include: 

  • straining to pass urine 
  • passing urine little and often 
  • restlessness, walking in and out of the litter tray 
  • passing urine in inappropriate places 
  • blood in the urine 
  • licking around the genital area or tummy 

It’s important to note: if your cat is straining to pass urine and nothing is coming out, this can indicate a ‘blocked bladder’. A blocked bladder is a life-threatening emergency, and you should contact your vet immediately. 

How does a vet diagnose urine crystals? 

If your cat is showing any signs of FLUTD, your vet will likely advise a urine sample. They may ask you to collect one at home, using a special cat urine collection kit. This consists of ‘pretend’ cat litter, that does not absorb the urine when your cat goes. You then collect the urine with a pipette, pop it in the sample pot, and take it to your vet. Or they may take a sample themselves, either by expressing your cat’s bladder or by using a needle to remove some directly from the bladder (through the body wall). This is called ‘cystocentesis’ and, while it sounds painful, most cats hardly notice! 

The vet will then perform a ‘dipstick’ on the urine, which tells them the pH, and looks for the presence of blood, protein and glucose in the urine. They will also measure the urine specific gravity (USG), which is the concentration of the urine.  

If your vet is suspicious of urine crystals or infection, they will then carry out a urine sediment exam. This involves spinning the urine in a centrifuge at high speed, so that any sediment sinks to the bottom. This is then dissolved in a little bit of urine and examined under a microscope. Your vet will be looking for crystals, bacteria, and blood cells. 

If your cat has severe or recurrent FLUTD signs and your vet detects lots of crystals in their urine, they may also recommend imaging (ultrasound and/or x-rays) to check for bladder stones. 

How do I get rid of crystals in my cat’s urine? 

If your cat is diagnosed with clinically significant crystalluria, your vet will recommend treatment to prevent more forming, and to prevent the formation of bladder stones. Some crystals/small stones can also be dissolved with treatment.  

Crystalluria in cats often requires a long-term management plan: 

  • Keeping the urine pH healthy and stable: usually through a prescription diet, with or without medications. 
  • Increasing water intake: feeding wet food, offering multiple water bowls (shallow ceramic dishes or full pint glasses are often popular, so their whiskers don’t touch the edges), water fountains, and keeping water bowls away from food bowls and litter trays. 
  • Home modifications to reduce stress and ensure your cat doesn’t hold their urine too long: making sure litter trays are in a quiet spot where your cat won’t be disturbed, having one litter tray per cat plus one spare, and avoiding scented litter. 

Your vet may well suggest a special urinary diet. 

What is the best cat food to help reduce crystals in urine? 

The best food for your cat will depend on what type of crystals they have, and if they have any bladder stones. You will need to feed ONLY the diet recommended by your vet and only water to drink. Otherwise, the diet will not work. 

Struvite crystals 

Your vet will suggest a diet that promotes acidic urine and is low in magnesium and phosphorous if it’s necessary to dissolve struvite. They will then recommend a diet suitable long term to prevent them recurring, if necessary. 

Calcium oxalate crystals  

Your vet will suggest a diet that causes alkaline urine, with reduced protein. If diet alone isn’t working, they may advise adding potassium citrate to ensure the urine pH stays alkaline. 

In all cases of crystalluria, ensuring your cat drinks plenty of water will help! The urine needs to be dilute to help prevent crystals from forming.  

You should never feed your cat a prescription diet unless instructed to do so by your vet. Not all urinary diets are suitable for all conditions or all cats. Different types of crystals need different diets. Some urinary diets can be fed long term, while others can’t.  

So, your vet will advise you on the best diet for your cat. 

How long does it take for crystals in cat urine to go away? 

This depends on the type of crystals, and whether your cat has any stones. It can be a few weeks, or a few months – and occasionally, stones may form that won’t dissolve and need surgical removal. Your vet will monitor your cat’s urine and symptoms to be sure the crystalluria resolves. 

Conclusion 

Crystalluria can be an incidental finding, for example in urine that is not fresh. Clinically significant crystalluria does not cause any symptoms on its own, but often happens as part of another lower urinary tract issue. Crystals in the urine need treating, to prevent the formation of bladder stones. The mainstay of treatment is a special prescription diet, increasing water intake, and reducing stress. Your vet will be able to advise you on the best diet for your cat.