What Do Brown Particles In Urine Of A Child Indicate?

My daughter is 5 and last Monday we took her to the dr. because i thought sha might have a bladder infection. She did, then two day later the called and the culture showed Ecoli. She went in today for another UA to make sure the infection was gone. Grandma had taken her and said that she notice brown flakes in the urine. When I got off work i had two messages from the nurse to call me. I can t call them back until tomorrow am now worried! What could it be?