Patients often times see clots in the urine and worry, that like clots in the blood stream, may go to the heart and lungs and cause a serious medical problem. Clots in the bladder are a problem only if they obstruct the flow of urine i.e. cause urinary retention.
Here is a podcast I did about how I got in trouble with a family trying to make this distinction…unfortunately in an unsuccessful humorous fashion. (From Urological Wit and Wisdom.)