From AMA guidelines:New and Established Patients
►Solely for the purposes of distinguishing between new and established patients, professional services are those face-to-face services rendered by physicians and other qualified health care professionals who may report evaluation and management services. A new patient is one who has not received any professional services from the physician or other qualified health care professional or another physician or other qualified health care professional of the
exact same specialty and subspecialty who belongs to the same group practice, within the past three years.
An established patient is one who has received professional services from the physician or other qualified health care professional or another physician or other qualified health care professional of the exact same specialty and subspecialty who belongs to the same group practice, within the past three years. See Decision Tree for New vs Established Patients.
Unless your providers are credentialled incorrectly, dermatology is a different specialty (not even subspecialty) than either internal medicine or gastroenterology. Most commercial carriers go by taxonomy codes. Medicare uses a much more limited 2 digit specialty code. Dermatology is clearly different than IM or GI; there is no overlap. You might have issues with IM vs GI depending on how the GI lists their specialty. Some GIs credential as both IM and GI.
I am part of a huge (hundreds of providers)multi-specialty health care system. Excluding Medicare, we use taxonomy to differentiate new vs established.