My 9 Year Old Daughter (68lbs) Has Had A Fever

My 9 year old daughter (68lbs) has had a fever for 2 days I took her to the doctor this morning and they found blood in her urine sample. She does not have a uti and no pain in her kidneys I have to go back in 2 days to have her give another urine sample. I am a concerned mother just wondering what it could be.