A range of causes may be involved in FLUTD. In some studies more than 50% of cases are idiopathic (cause not defined). Viruses and stress releasing free radicals into the urine have been postulated as potential factors in these cases. Known causes of FLUTD include urolythisis (stones in bladder), and bacterial infection.

Urolythiasis results from the formation of crystals in the urine. The most common crystals are magnesium ammonium phosphate, also known as struvite. Other crystals include calcium phosphate, calcium oxalate, uric acid and cystine. Male cats are almost exclusively effected by crystal formation often as a result of a plug of struvite and mucus blocking the urethra at the tip of the penis. True urolythiasis is where the crystals combine to form calculi (stones) within the bladder and urethra.

The factors affecting stuvite formation include the concentrations of magnesium, ammonium, and phosphate ions, and the pH of the urine. Where pH rises above 7.0 crystals can form and calculi will grow. Between 6.4 and 7.0 crystals will be stable however calculi formation is less likely. Below pH 6.4 crystals will generally dissolve.

Restriction of dietary magnesium is used in diets to treat and prevent FLUTD however there is some doubt about whether this is effective. Controlling pH is considered to be the most important factor in treating FLUTD. Meat diets generally result in acid urine however there is a phenomenon known as the post-prandial alkaline tide. This is where the act of eating causes the secretion of acid into the stomach which in turn results in alkalosis (high pH) in the blood. This is balanced in the body by the excretion of alkaline urine. Diets and supplements designed to combat this effect produce ammonium chloride or an acid urine at the time of feeding.

Treatment of cats which have become obstructed represents a medical emergency. Apart from signs of persistent unproductive to urinate these animals may have signs of kidney damage with depression and vomiting. The obstruction of the urethra must be back-flushed to the bladder usually under general anesthetic and a catheter (plastic tube) is introduced and sutured in place. The catheter remains for 3-4 days while the cat is maintained on intravenous fluids (drip). Antibiotics are generally administered however there is little evidence that bacteria play much of a role in the condition other than secondary to having an indwelling catheter. Urinary acidifiers are used to create the desired pH in the urine.

A number of environmental factors have been proposed as risk factors for the development of FLUTD. There is a genetic predisposition in the Persian breeds of cats. Castration causing a narrowing of the urethra is unlikely to be important as entire male cats can be effected Dry food was implicated in the past both for the formation of alkaline urine and for concentrating the urine. Most dry food manufacturers have addressed these problems and this is no longer considered a risk factor.

It is of interest to not that there has been an increasing incidence of calcium oxalate based FLUTD. These crystals tend to form in moderately acid urine and the increase may be a result of the focus of feeding to produce acid urine.