According to the CPT® book, E/M services are divided into categories and subcategories. Office services are divided into new and established patient visits. Consultations are divided into outpatient/office consults and inpatient consultations.  The E/M services typically have three to five levels of services and these levels are not interchangeable from one to the other.   That is, a level one established patient visit is not equivalent to a level one admission.

Besides including office services, hospital, nursing home services and consultations, the E/M services also include preventive medicine services, critical care and newborn care.

Most E/M services have three components; history, exam and medical decision making. Some of the codes have typical time assigned to them. Some codes do not have typical times, such as observation, emergency department visits and preventive medicine services. Most of the hospital services are defined as per-day codes while the office services are per-visit codes.

A typical E/M service is listed in the CPT® book as requiring either two of three of the three key components or three of three of the three key components. The key components are history, exam and medical decision making.

The CPT® book also lists for each code:

•    The typical time when time may be used as a factor in that code and

•    The type of presenting problem or the nature of the problem that the physician would be addressing.

For example, code 99213, requires two of three of the following components: an expanded problem-focused history, an expanded problem-focused exam and low medical decision making.

The descriptions of the levels of history, exam and medical decision making are found in the Documentation Guidelines and not in the CPT® book.  There are articles in Codapedia  discussing using time to select an E/M code, E/M profiles, the general principles of documentation, and the Documentation Guidelines.