The cause of FUS is unknown. Diet has been incriminated as a factor influencing the severity of the problem. Infection and stress may also be factors. Excessive amounts of magnesium in the diet that produces a basic urine has been shown to cause struvite crystals to form and produce the disease in laboratory cats. Diets have been formulated to reduce the struvite crystals by acidifying the diet and seem to be effective. However, these diets that produce acid urine may predispose to oxalate crystals. Other types of crystals and debris could also be responsible for the urethral blockage. Urinalysis is helpful to determine the type of crystals and the acidity of the urine. This helps the veterinarian to decide proper treatment. Analysis of the obstruction causing material is the most accurate way of knowing the cause.