The fact is that the diagnostic criteria for ADHD have already been in existence in the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (Text-Revision), referred to as DSM from this point forwards. This is the book, published by the American Psychiatric Association, which mental health and medical professionals refer to for making diagnostic decisions in this particular subject area.
While a primary care clinician can easily refer a patient for a sleep apnea study and order other tests to rule out a physical cause of ADHD-like symptoms, what primary care clinician is going to have the time to go over all 18 symptoms, interview teachers and other sources of information, evaluate for a learning disorder, and evaluate for psychological causes of the symptoms? None who I know of. For example, evaluating for a learning disability is going to require time intensive psychological testing and primary care clinicians simply do not administer IQ tests and test of academic achievement.