There are several different ways to handle this. I am assuming this is a new patient to your practice, you can bill out a D0150 as long a comprehensive exam is completed with the normal gathering of medical/dental and general history. Or you could also bill a D0145 before the age of three if counseling (Examples D1310 and D1355) is completed in conjunction with an examination. Once the patient has reached the age of three, you can bill a D0150 keeping in mind that an insurance company may downgrade this to a D0120 as this is now an established patient to your practice. If I am wrong in any aspect, please let me know.
