Glossary

Bladder crystals

Microscopic mineral particles in urine that can clump into stones and irritate or block a cat's urinary tract.

Also called: struvite crystals, calcium oxalate crystals, uroliths, bladder stones, urinary stones

Bladder crystals are tiny solid particles that form when minerals in urine become too concentrated or the urine chemistry shifts. The two common kinds in cats are struvite and calcium oxalate. Crystals can combine into larger stones, called uroliths, that rub the bladder wall or lodge in the urethra.

Some crystals cause no trouble, and a few appear in the urine of healthy cats. Others come with the signs of FLUTD: straining, frequent trips to the litter box, blood in the urine and urinating in odd places. In male cats, crystals and mucus can form a plug that causes a urinary blockage, which is an emergency.

A vet finds crystals by examining a fresh urine sample, and may use X-rays or ultrasound to look for stones. Management depends on the type. Struvite stones can sometimes be dissolved with a prescription diet. Calcium oxalate stones do not dissolve and may need to be removed by surgery or other procedures. The diet also helps prevent new crystals, and encouraging a cat to drink more can dilute the urine. Never change a cat's diet on your own, since the wrong food for one type can worsen another. Ask your vet which type your cat has and what follow-up tests are needed.

Last reviewed November 7, 2026

In the index now

Related terms

FLUTD An umbrella term for the conditions that cause pain, straining and bloody urine in a cat's bladder and urethra. Urinary blockage A life-threatening emergency in which the urethra is plugged so a cat cannot pass urine, most often in male cats. Cystitis Inflammation of the bladder, which in cats is often stress-linked and has no infection or stone behind it. Urinalysis A set of tests on a cat's urine that reveals kidney function, infection, crystals, diabetes and more. Chronic kidney disease A gradual loss of kidney function, common in older cats, that can be managed for months or years but not cured.