In answer to your first scenario question, using the codes you've used in your example, the codes would be preventative service for new patient (99386) and the appropriate level of service for a
follow-up (or established patient) office visit, not a new patient office visit code, because the patient is no longer "new" for this second E/M encounter. The -25 modifier is used to indicate that this is an unrelated evaluation and management service by the same physician on the same day of a procedure or other service...the preventative exam in your example. This helps the second service to bypass computer edits and be considered for payment. Without the -25 modifier, it would be denied because the computer would have already processed a claim for this same patient, by the same physician on the same day.
In your second scenario patient coming in for visit and vaccinations, no -25 modifier is required on the E/M service code. This combination of billing (E/M encounter/visit with vaccinations) is common and so it was decided that the -25 modifier would not be required for this kind of scenario, nor is a -25 modifier required on the E/M service code, when billing for an encounter in which lab services are also performed.
I hope that helps!
MaryAnn Dimitrov, CPC, CPC-H, CCS, CCS-P, AHIMA-Approved ICD-10-CM/PCS Trainer,
President, Medical Basix
md@medicalbasix.com