Let me begin by stating that any abnormal test report needs to be probed further in the background of patient's symptoms.
Coming to your son's urine reports although you have not mentioned any symptoms,but i would like to take it further.
First step will be to do a repeat test of urine if abnormality still persists then further evaluation will be required .
The cause of this abnormal finding can be anywhere starting from kidneys to tip of urethra
You should immediately get thorough evaluation done.