There are other articles on CodingIntel about the difference between new and established patients, and the rules haven’t changed, but that doesn’t mean it is always clear. I hope this blog post clarifies the issue.
“Interpret the phrase “new patient” to mean a patient who has not received any professional services, i.e., E/M service or other face-to-face service (e.g., surgical procedure) from the physician or physician group practice (same physician specialty) within the previous 3 years.
For example, if a professional component of a previous procedure is billed in a 3 year time period, e.g., a lab interpretation is billed and no E/M service or other face-to-face service with the patient is performed, then this patient remains a new patient for the initial visit. An interpretation of a diagnostic test, reading an x-ray or EKG etc., in the absence of an E/M service or other face-to-face service with the patient does not affect the designation of a new patient.”
“Solely for the purposes of distinguishing between new and established patients, professional services are those face-to-face services rendered by a physician and reported by a specific CPT® code(s). A new patient is one who has not received any professional services from the physician or another physician of the exactly same specialty and subspecialty who belongs to the same group practice within the past three years.”
From CPT®: “When advanced practice nurses and physician assistants are working with physicians, they are considered as working in the exact same specialty and same subspecialties as the physician. “
When physicians enroll in Medicare and private insurance companies, they self-designate their specialty This is typically the same as their board certification. CMS has a list of two-digit specialty designations that they use at enrollment and to process claims. Although there are more specific taxonomy specialty codes, CMS uses the two-digit code to process claims.
Enrollment and credentialing for non-physician practitioners (NPPs), and claims processing, is done differently by Medicare and commercial carriers. Medicare enrolls all nurse practitioners, working in any specialty, as nurse practitioners. Medicare enrolls all physician assistants, working in any specialty, as physician assistants. They are not enrolled based on the specialty in which they are working.
Most commercial payers enroll NPPs based on the specialty in which they work, and make a distinction between NPPs working in primary care and those working in specialty practices. This allows the payer to assign different co-pays for visits done by NPPs working in primary care and specialty practices.
The CPT® rule is to consider NPs and PAs as working in the exact same specialty as the practice in which they are assigned. “When advanced practice nurses and physician assistants are working with physicians they are considered as working in the exact same specialty and exact same subspecialties as the physician.” 
Although neither CPT® nor CMS define group membership in their definitions, physicians who report claims with the same tax ID are considered to be in a group.
New versus established
A patient who is sent from Internal Medicine to Orthopedics is considered a new patient, if the patient has not been seen in the past three years. This is true if the clinician who saw the patient in the IM practice was a physician, NP or PA. There is a decision tree in the CPT® book that can be helpful in determining if a patient is new or established.
- Claims processing, specialty and group membership
Initial visits to different specialty physicians are processed as new patients, if the patient has not seen a physician in that specialty, in that group, in the past three years.
- Claims processing for NPPs
Commercial insurers usually follow the CPT® rule and consider the NPP as being of the exact same specialty as the physician (s) with whom they practice. As mentioned, insurance policies sometimes have a different deductible and different benefit categories for primary care and specialty services. The company considers the PA who works in an orthopedic office as a specialty provider and the PA who works in a Pediatric practice as a primary care provider. This allows them to process claims depending on if the visit is done in a primary care or specialty practice.
However, since Medicare considers all PAs of the same specialty, and all NPs of the same specialty, they process claims differently. In a multi-specialty group, if a patient sees an NP in oncology, that patient will be considered established if seen by any other NP working in any specialty. This can be challenging in a multi-specialty group if new patients are seen by NPs and PAs.
Not all specialties are represented
Then, there are the problems caused by subspecialties not recognized by Medicare. This is a common problem in general surgery. There are surgeons who specialize in breast conditions or trauma, and these two subspecialties don’t have a CMS specialty designation. Since there isn’t a CMS recognized subspecialty, then all three of those types of surgeons in the same group will be considered as general surgeons.
Or an internist may provide primary care services and specialize in infectious diseases, as well, even without a board certification. But, for the purposes of claims processing, only one specialty designation can be selected and is used in claims processing. The internist who has an interest in infectious disease and treats those patients who is signed up as an internal medicine physician will have claims processed as an internist.
 CPT® 2018 Professional Edition, AMA, Chicago, page 4