What medication is he taking for the ADHD?
Does he take medications for ADHD?
The kidney secretes and uses several enzymes. The first being erythropoietin, an enzyme that stimulates the production of red blood cells in the bone marrow in response to low oxygenation in the blood. This is regulated by the blood flow through the kidney, and the kidney decides how much to secrete. More RBC are needed when oxygenation to the tissues is low, does your son have asthma, or circulation problems?
Renin is an enzyme that controls blood pressure, and is secreted from the kidney in response to reduced arterial blood pressure, low oxygenation(blood flow) to kidneys, dehydration, or high salt diet. It increases blood pressure by constricting the arteries. So this blood pressure dysregulation is usually the main concern with kidney issues. I would first recommend a low salt diet (sorry!).
Prostaglandins are also activated in the kidney, but these are intended to reduce blood pressure, counteracting the effects of renin.
So long story short, how is your son's blood pressure? (avg=120/ 80) Hypertension= 140/90 or above. Does he have chronic conditions causing low oxygenation (diabetes, asthma, live in high altitude, and you say he had blood work, do you know what the oxygen concentration in his blood was (pO2)?
Almost forgot, see if the medication side effects affect blood pressure, heart rate, oxygen concentration, exc.
Hope this helps! But I would advise asking your doctor because he has access to your son's health history, lab values, exc.