Proteinuria in a 15 yr old male

My 15 yr old son had a urinalysis done as part of a routine check-up and was found to have a protein reading of 2+. His doctor advised me to collect his first morning's urine 3 days after the first test, keep it in the refridgerator for the day and bring it in to his office when they opened at 5PM to have it sent to a lab to be re-checked. This result was also 2+. We were called into the office and advised that my son has proteinuria and that he has to get further tests in both his urine and blood and then most likely see a kidney specialist and possibly have a renal biopsy done. Of course, I'm very concerned over this. My son appears to be in excellent health, is very atheletic and his intial bloodwork was fine. No blood was found in his urine.I have read that proteinuria is common finding in teenage boys and in most cases it is a benign condition, even if it is persistent and only a small percentage of teenagers actually have an underlying kidney disease. Any advise on how to cope with this and help my son stop worrying is appreciated. Thanks.