I Had A Complete Bloodwork Test As I Do Every

I had a complete bloodwork test as I do every 6 months. A trace of blood showed in the urine test. I am to get another test in a few weeks. My family doctor who is new to me, wanted me to see an urologist. I looked at my results from the bloodwork 6 months ago and it also showed a trace of blood but my doctor then wasn't concerned. What would cause this as I don't have a bladder infection? I do get them but it has been many months ago. Nothing was bad with the kidneys. I am concerned. Thank you.