Just got blood test results for my son. Everything was normal except for a slightly elevated bilirubin of 1.7. He is 13 years old, 5'4", and weighs 133lbs. His diet is balanced. His activity includes 2 hr martial arts classes twice a week, which he has been doing for 6+ years, but has been unable to complete for the past month. He lasts about an hour then gets so fatigued he needs to sit down. During these episodes of extreme fatigue, he becomes pale and gets dark circles under his eyes, and he complains of muscle weakness. His doctor seems unconcerned, but I am. Should I insist on further blood tests?