It's not uncommon to see crystals in cat or dog urine. In fact, crystals are so common as to be considered normal in some pets. When the crystals become overly abundant or when abnormal types of crystals present themselves, however, they may cause problems or indicate the presence of disease.

Crystals are typically most problematic for the urinary system, but the underlying issues leading to urine crystal formation often originate in other parts of the body.

How Urinary Crystals Form

If you can remember back to your high school chemistry class, you'll recall that crystals will form in solutions when there's an overabundance of certain molecules — think of salt crusting a bucket of ocean water after the water has evaporated. Crystal formation also depends on the temperature, the concentration of certain compounds and the acidity of the urine.

Pet parents often confuse urinary crystals with urinary stones, or uroliths. Urinary stones are similar to human kidney stones, which is less common in dogs and cats but typically form in the bladder. Urine crystals and stones aren't always related. Certain kinds of crystals in cat urine or dog urine may eventually lead to stone formation.

The cause of crystals in cats and dogs depend on the kind of crystal your veterinarian finds. In general, crystals are found when an abundance of certain compounds are excreted by the kidneys. These molecules can be overabundant in the case of liver diseases, poisoning and genetic conditions, among other causes.

Crystals in Cat Urine vs. Crystals in Dog Urine

Dogs and cats are different in many ways, but both seem predisposed to urine crystal formation. The crystals themselves are nearly identical. The difference lies in the kind of crystals that form in dogs or cats and how they can adversely affect these pets.

Wag! notes that while the presence of crystals in dog urine may indicate an underlying disease, the crystals themselves don't usually hurt a dog. In cats, the small size of the urethra means that crystals can clump and block the flow of urine.

The Cornell Feline Health Center notes that crystals in cat urine are sometimes associated with a range of urinary diseases collectively called feline lower urinary track disease (FLUTD). The signs of FLUTD may include:

• Bloody urine
• Straining to urinate
• Crying or vocalizing while using the litter box
• Urinating less than normal
• Urinating outside the litter box

If you notice any of these signs you should take your cat to the vet immediately. Your vet will check for and identify any crystals in your cat's urine and evaluate her for any associated diseases. Every time a pet's urine is thoroughly examined, a microscopic search for crystals is part of the equation. Your vet may also suggest blood testing and X-rays.

Common Types of Urinary Crystals

Crystals in cat and dog urine are often one of several common types:

• Ammonium urate: Most commonly found in dog urine, an abundance of these crystals may signal liver disease, according to Vet Times. Certain breeds like English bulldogs and Dalmatians are predisposed to these crystals. While rare in cats, some can be predisposed to this condition due to genetic issues or defects.
• Struvite (magnesium ammonium phosphate): Low numbers of struvite crystals are considered normal for some dogs and cats. They occur most commonly in alkaline urine or urine that's not fresh. They can also be associated with infection, which is one of the things your vet will test for if they find crystals in your pet's urine. Struvite crystals in cats can form plugs that lodge in the urethra and lead to urinary obstruction. They can lead to urinary stones in both dogs and cats.
• Bilirubin: Lighthouse Veterinary Consultants notes that bilirubin crystals indicate possible liver problems in cats. They can be present in otherwise healthy dogs if the urine is concentrated, especially in males.
• Calcium oxalate: Pets excreting too much calcium or oxalic acid in their urine can form these crystals. These can also be found in normal urine, particularly if it's acidic or refrigerated. These crystals can also indicate infection if the pH in the urine is low and can be associated with calcium oxalate stones. Although rare, they can form urethral plugs in male cats. International Cat Care notes that toxic loads of calcium oxalate are a sign of poisoning from antifreeze, which cats can accidentally lick off a floor or open bottle. There is still a lot to learn about these types of uroliths as they associated with a complex and incompletely understood sequence of events.
• Cystine: Uncommon in both dogs and cats, these crystals can be seen in dogs with an inherited tendency to excrete the amino acid cystine. Dogs who form these crystals also have a possibility of forming stones, according to the Minnesota Urolith Center.