If reason for new patient visit is the preventive care, then 99385. Modifier 25 indicates that on the day of a procedure like a preventive care visit, the patient's condition required a significant, separately identifiable E/M service, above and beyond the usual pre and post-operative care associated with the procedure or service performed.
Use Modifier 25 with the appropriate level of E/M service. So in this case,
99385 Dx: V----- for new patient preventive check, then
Established patient 99213-25 for Dx: 462.-- or whatever illness.