feline lower urinary tract disease/ feline urological syndrome (flutd/ fus)

This is a blanket term that refers to urinary tract disease caused by a variety of things. Signs include straining to pass urine, blood in the urine, passing small amounts and crying out when urine is passed. Stones (or calculi) may have formed from crystals and be causing an obstruction but sometimes there are no stones or obstructions and the disease can be due to bacterial infection, or to a form called 'Idiopathic' where no one knows the real cause. Some cats appear to be prone to developing this condition and it may be exacerbated by stress.

SOURCE: cats.org.uk