Protien in urine during pregnancy?

I recently went to my OB for check up at 18 weeks. They had a slew of lab results including a 24 hour urine. They said I have a UTI (w/o symptoms) and high levels of protien in my urine but too much to be from UTI. My blood pressure was slightly high so now i am advised to have a low salt diet and take BP meds. I asked him if the protien could be from the UTI and he said no but from what I have read UTI can cause high protien in urine. How does he know the difference? should I be overly concerned? Isn't it possible that if it is a long standing UTI it has reached my kidneys and that is the cause?