A Crystal Ball in Your Cats Urine

Urinary crystals mean watch for urinary stones

Finding crystals in a urine sample can be a warning that painful urinary stones and/or deadly blockages may be forming. Persian and Himalayan cats have an increased risk for urinary crystals and stone formation.

The most common types of crystals are struvite and calcium oxalate, and these can be distinguished by their unique shapes under a microscope. Each type requires different treatment, so a urine analysis is important.

Urine samples need to be fresh—ideally examined within 30 minutes. Your veterinarian may do a cystocentesis (using a needle to draw a sample through the abdominal wall) to get a truly fresh, unadulterated urine sample.

Struvite Crystals

Made of magnesium ammonium phosphate, struvite crystals are usually found in clean urine. They rarely have an infection associated with them, so there’s often no need for antibiotics. Struvite crystals can usually be managed successfully to prevent the formation of struvite stones (see “What You Can Do” sidebar).

There are some illnesses that may predispose a cat to struvite crystal formation. Cats with idiopathic cystitis (bladder inflammation of unknown cause) may have struvite crystalluria (struvite crystals in the urine). Chronic use of diuretics, some kidney problems, and the use of antacids may increase your cat’s risk of developing these crystals.

Struvite formation occurs in an alkaline pH, so your veterinarian may recommend a change in diet to one that promotes healthy acidic urine. A cat’s normal urine usually has a pH between 6.0 and 6.5. (Remember chemistry 101? 7.0 pH is neutral; anything below that is acidic and anything above 7.0 is alkaline.) If your cat refuses to change diets, you may need to give a urinary acidifier such as methionine.

There are prescription diets, such as Hill’s Prescription Urinary Care s/d, that can dissolve struvite stones. These diets are generally fed short term, as long as needed to dissolve any struvite stones in your cat’s bladder. If your cat has repeated urine samples with struvite crystals, your veterinarian may prescribe a specific long-term diet designed to prevent crystal/stone formation.

Calcium Oxalate Crystals

Calcium oxalate crystals tend to develop in older cats. Male cats are at a higher risk, especially neutered males. Unlike struvite, calcium oxalate is more likely to form crystals in acidic urine.

High levels of calcium in the blood can predispose a cat to form calcium oxalate crystals. Excessive consumption of vitamin D and/or sodium can also influence the presence of these crystals. Ethylene glycol (antifreeze) poisoning can cause formation of calcium oxalate crystals.

Using potassium citrate can help to raise the urinary pH. Vitamin B6 supplementation may also help. There are normal bacteria in feline intestines called Oxalobacter formigenes that survive by metabolizing oxalate. The population of this bacterium is affected by many antibiotics, so using medications only as needed can help to maintain helpful gastrointestinal flora. Prescription diets won’t dissolve calcium oxalate crystals or stones, but they can help maintain an ideal pH in the urine.


Important aids in avoiding any crystal or stone formation include encouraging drinking and feeding canned food so your cat intrinsically takes in more liquid.

While crystalluria doesn’t represent an emergency by itself, it is a warning that your cat could develop urinary calculi or stones that may lead to a blockage. Urinary blockage is a medical emergency.

If your cat is straining in the litterbox but not passing urine or passing tiny amounts, he could be blocked. Watch for frequent trips to the litterbox with little urine produced as well as any hematuria (blood in the urine). Passing small amounts of urine outside the litterbox can also be a tip. When in doubt, consult your veterinarian.