Urination and Kids

Hello everyone, I have a concern that bothers me and my husband. Our 9 y/o son would not go to Bathroom to urinate sometime for more than 10 to 12hrs. We have to push him to drink water and then keep on nagging him to use bathroom to pee; but he will say pee is not coming. Last year we talked to a pediatrician who did blood test and urine test and told us "test results were normal". Pediatrician told us he may have higher bladder capacity. Should we loose our sleep over this or this is a normal 9 y/o behavior? Can some one shed some light and if they have similar experience at home, it would be greately appreciated.
Concerned Mom