blood in my 8yr old sons urine

today my son son had blood in his urine. i did not see it but my older son did and said it was a red pinkish color. my son is very active and runs around alot, jumping, climbing, and so on. i have read that people who run/jog sometimes have bloody urine. i am wondering if this could be the reason for my sons bloody urine. he has no other symptoms, no fever, fatigue, pain, swelling,.... i have schuduled an appointment with his doctor but i am hoping for some answers here, thank you