Crystals in Dog and Cat Urine: what you need to know.

Published by Dr. Patty Khuly
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min read

It’s not uncommon for tiny crystals to form in the urine of some cats and dogs. These are so small that you need a microscope to see them but they can still cause problems. Depending on the cause they may or may not be something to be concerned about. Sometimes it’s a simple infection that is easily treated but other times, crystals can be a sign of disease elsewhere in the body or environmental problems like cats being stressed about their living situation.

White Chihuahua peeing on a pole at the beach

Why do crystals form in urine?

One of the kidneys’ major jobs is filtering the blood to keep certain minerals like sodium, phosphorus and calcium at safe and healthy levels. This means that it is normal for urine to have some minerals in it. These are flushed out every time the animal has a wee. Crystals form if something changes to upset this careful balance. It may be that too much of a certain mineral appears or the urine becomes too concentrated. Imagine a cup of tea. You add a teaspoon of sugar and stir it in. The sugar dissolves and disappears from view. Keep adding more and more and eventually there isn’t enough tea to hold all the sugar and it will become visible as crystals. You either need more tea or less sugar to solve the problem.

Are urinary crystals a problem?

In some pets, a few microscopic crystals can be quite normal and may never cause a problem, but there are times that we certainly do need to worry about the presence of crystals. In some cases they are a sign of things like liver or kidney disease, bladder infection, poisoning, stress or inherited problems in breeds like in Dalmatians and bulldogs.

Although crystals are microscopic there are signs you can watch out for that can alert you to their presence. These are usually signs of cystitis (inflammation of the bladder), which some of you might have experienced yourself. If you have, you’ll know how unpleasant it is. Signs may include;

  • Blood in the urine
  • Trying to urinate more frequently than usual but not passing much
  • Crying or vocalising while trying to urinate
  • Urinating in unusual places or loss of house-training
  • Straining to urinate

Sometimes crystals can cluster together and form stones and these can cause damage and inflammation and, especially in male animals with their narrower urethra, block the flow of urine altogether. This is a medical emergency. We see blockages most commonly in male cats because the urethra is so narrow it’s easily clogged with crystals, tiny stones or even just inflammatory cells that act like a plug. If an animal stays blocked for more than a few hours they can go into kidney failure or rupture their bladder, both of which can be fatal. If your pet is showing signs of cystitis they need to see a vet but if they can’t pass urine at all you need an emergency appointment without delay.

Not all crystals are created equal.

There are several different types of crystals that can form in urine and they are caused by different diseases and processes. Let’s take a look at them, starting with the most common ones first.

  • Struvite. These are also called magnesium ammonium phosphate or MAP, because these are the minerals that form them. They are usually caused for very different reasons in dogs vs cats. In dogs, they are virtually always a result of a urinary infection. The bacteria make the urine more alkaline than it should be and the struvite crystals can form - they can’t form in acidic urine. But before talking about crystal types, a few words about a term you may also have heard, 'Feline Lower Urinary Tract Disease' (FLUTD). FLUTD is a name for all the diseases of the cat's bladder and urethra, which all have the same symptoms in common, which we described before. All stones and crystals which we will talk about later are included in the 'FLUTD group'. But the most common cause of FLUTD is in fact feline idiopathic cystitis (FIC), a complex disease that is associated with stress. You can read more about FLUTD here.
  • Calcium oxalate. Animals with excess calcium, citrate or oxalates in their urine may form these crystals and stones. They are also seen associated with some diseases such as hypercalcaemia and some cancers. Calcium oxalate stones also seem to like to form in the kidneys as well as the bladder. Some breeds like Yorkshire terriers, schnauzers and Lhasa Apsos are prone to these stones more than other breeds.
  • Ammonium urate. In both dogs and cats these crystals and stones can be a sign of liver disease. Blood tests will help your vet see if this is the cause and they may also want to do a liver biopsy to find out more. However, we see these types of crystals most commonly in certain breeds as an inherited problem. The most common ones are Dalmatians and English bulldogs.
  • Cystine. These are the least common of the four and are most often seen as an inherited problem in breeds such as the English bulldogs, dachshunds, bassets and Newfoundlands. They are almost always in male dogs and may be affected in some cases by testosterone.

How do we treat urinary crystals and stones in cats and dogs?

As you probably will have guessed, different types, with different causes, need different courses of action. What you might not have guessed is that therapeutic foods can help in the treatment of all of them.

Firstly, your vet will need to get to the bottom of what type of stone crystal you are dealing with and whether there are underlying issues. They will need a fresh urine sample and will almost certainly want to do blood tests and possibly imaging to make sure there are no stones.

Treatment for causes will need to be started. This might be antibiotics for a bladder infection or addressing stress in the case of struvites or treating liver disease in the case of ammonium urate.

Your vet will almost certainly advise a therapeutic food. In the case of all of the above, except calcium oxalate stones, these foods can dissolve crystals and stones if used correctly alongside other treatments. Calcium oxalate stones will need to be removed surgically, where possible, and then a food can be used to prevent recurrence. These foods have many benefits such as altered mineral content, targeted pH levels for the urine, omega3 oils from fish oil to fight inflammation, and some also have natural additives to help reduce stress.

Water intake is also hugely important. Remember the cup of tea we mentioned at the beginning? Good water intake keeps the urine throughput high and means that minerals are flushed through before they can start to form crystals and stones. Talk to your vet about the best ways to increase water intake. This could be with wet food, soaking kibbles or using things like water fountains.

As always, if you have any concerns about your pet, or something just doesn’t seem right, take them to your vet. It’s never a waste of time and catching things early is always better than waiting until it’s too late.

Contributor Bio

Dr. Patty Khuly

Dr. Patty Khuly is an honours graduate of both Wellesley College and the University of Pennsylvania School of Veterinary Medicine. She received her MBA at The Wharton School of Business as part of the prestigious VMD/MBA dual-degree program. She's now the proud owner of Sunset Animal Clinic in Miami, Florida. But that's not all. Dr. K is a nerdy reader, avid knitter, hot yoga fanatic, music geek, struggling runner, and indefatigable foodie. She lives in South Miami with three dogs, countless cats, two rescued goats and a hilarious flock of hens.

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