If he lost weight he must do more analyses (should check for
parasites in fezes, do you have animals
at home?). My sons ENDO asked that to my son, also full blood tests (with liver enzymes, cholesterol, etc.), free testosterone, PH, etc. (hormones for puberty) and urine analyses. May be you should ask your sons Ped to repeat the analyses (more complete), and then you will have more information for the ENDOs appointment.