The red blood cell count (commonly referred to the hematocrit) can be high because of several things. The first question I would have is how high was his hematocrit. Having a slightly high hematocrit can be a normal finding in a young man especially if he is in good shape.
An abnormally high hematocrit can have a few causes. People that live at high altitudes have an abnormally high hematocrit. In addition, athletes that "blood dope" with erythropoietin get high hematocrit's. A rare blood disorder called polycythemia vera causes an abnormal production of red blood cells which can be dangerous. This is the most concerning possibility and will need to be diagnosed soon if it is the problem.
The type of doctor
you should see really depends on how high his hematocrit is. This will be a judgment call by your son's primary care physician
. I would say that if he was my patient and his hematocrit was above 50%, then I would consider referring him to a hematologist
. If it is below this amount (and thus just slightly above normal), then I would probably just repeat the test in a few months. Since your son's doctor is familiar with his past medical and family histories, he or she is most equipped to make this call. Good luck.