Finding blood in the litter tray or, worse still, on the carpet is guaranteed to trigger concern. A cat running back to the litter tray every 5 minutes and sitting with a concentrated look on the face is also a major worry.
In a young male or desexed male it is an emergency as he may have a blocked or semi-blocked urethra and be unable to pass urine. The bladder rapidly fills and the cat can become toxic in a matter of hours.
The main cause of blood in the urine is stress and the resulting pain from an inflamed bladder. Stress or anxiety cause the inflammation which is painful, causing more stress... and the vicious circle goes on. Common causes of stress are moving house, new people or pets in the household, tradies or visitors in the house, conflict between household cats, or any change in routine.
In older cats, especially those with kidney disease, diabetes, or hyperthyroidism, a urinary tract infection is more likely. Occasionally bladder stones cause blood in the urine.
After a chat with you and a physical examination of your cat, your vet will take a urine sample to sort out what is the most likely cause of the problem.