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Uroliths (Bladder Stones) in Cats

Most bladder stones in cats cause symptoms of FLUTD. The same process that causes small crystals or crystalline material to plug the urethra also causes stones to form in the bladder. Stones are more likely to form in a persistently infected bladder and in a bladder that is partially obstructed. Stones irritate the bladder wall, prolong infection, and produce symptoms of FLUTD. Cats with bladder stones may not have any crystals present in urine samples. Some affected cats show no clinical signs.

The two most common types of uroliths are struvite (magnesium phosphate) and calcium oxalate. There are also other types of uroliths. Two factors of primary importance in struvite stone formation are high concentrations of magnesium in the urine and a urine with an alkaline pH (over 6.8). Factors of primary importance in calcium oxalate urolith formation include urine with an acidic pH and lower levels of magnesium in the diet.

Female cats have a higher risk of developing struvite uroliths, especially female cats 1 to 2 years of age. However, struvite uroliths have been found in kittens as young as 1 month and cats as old as 20 years. Calcium oxalate uroliths tend to occur more often in male cats, particularly 10- to 15-year-old neutered males.

General Feline Urolith Facts


Calcium Oxalate

Female cats

Neutered male cats

1 to 2 years of age

10 to 15 years of age, Persians, Himalayans, Burmese predisposed

Alkaline urine is a risk

Acidic urine is a risk

About 50 percent of all uroliths

About 39 percent of all uroliths

More than 85 percent of all urethral plugs

Less than 15 percent of all urethral plugs


The Minnesota Urolith Center at the University of Minnesota College of Veterinary Medicine, established by Dr. Carl A. Osborne, is well known for its work on uroliths in cats. Among other things, the center analyzes uroliths removed from cats and sent in for study. From 1981 until about 2002, the percent of struvite uroliths dropped from close to 98 percent to just 33 percent. This is undoubtedly due to changes in feline diets that led to acidic urine.

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