4.1 CPT structure & E/M coding

Current Procedural Terminology at a glance

CPT (Current Procedural Terminology) is the code set used to report medical, surgical, and diagnostic procedures and services. It is developed, maintained, and copyrighted by the American Medical Association (AMA) — not by CMS. The CPT Editorial Panel reviews change proposals throughout the year, and a new edition is published annually that takes effect January 1.

Keep the division of labor straight for the CBCS exam: ICD-10-CM explains why the patient was seen (the diagnosis), while CPT explains what the provider did (the procedure or service). On the CMS-1500 claim the CPT code is entered in block 24D and drives the charge; the ICD-10-CM code sits in block 21 and is pointed to from block 24E to establish medical necessity.

Five-digit structure

A standard CPT code is five characters long. Category I codes are five numeric digits with no decimal point — for example, 99213 (established-patient office visit) or 27447 (total knee arthroplasty). Up to two modifiers (two characters each) may be appended to add detail without changing the base code; modifiers are covered in section 4.2. Because codes are grouped by range, the leading digits hint at the type of service, but always confirm the full descriptor in the book rather than guess from the range.

The three categories of CPT codes

• Category I — the main body of five-digit numeric codes for widely performed, FDA-approved procedures and services (the six sections below). These are what you report on most claims.
• Category II — optional four-digit codes ending in the letter F (e.g., 3044F) used for performance measurement and quality tracking. They are supplemental, carry no fee, and are never required for reimbursement.
• Category III — temporary four-digit codes ending in the letter T (e.g., 0512T) for emerging, experimental, or investigational services and technology. When enough evidence accumulates, a Category III code may be converted to a permanent Category I code.

The six sections of Category I

Notice that Evaluation & Management is printed first in the book and used most often, even though its code numbers (the 99000s) are numerically the highest. That ordering is deliberate: E/M services are so common in outpatient billing that the panel placed them up front for quick access.

Evaluation & Management (E/M) coding

E/M codes describe cognitive services — the provider taking a history, examining the patient, and making decisions — rather than a hands-on procedure. The most heavily tested E/M concept on the CBCS is the difference between a new and an established patient:

• A new patient has not received professional services from that provider, or from another provider of the same specialty in the same group, within the past three years.
• An established patient has been seen within the past three years.

New-patient office visits use codes 99202–99205; established-patient visits use 99211–99215. New-patient visits generally reimburse more because more work is needed to gather a first-time history.

The 2021 office-visit revisions

A landmark change took effect January 1, 2021 for office and outpatient E/M (99202–99215). Coders no longer count history and exam "bullets" to select a level. Instead the level is chosen by either:

1. the level of medical decision making (MDM), or
2. the total time the provider spends on the encounter that calendar day, including non-face-to-face work such as chart review and documentation.

Medical decision making is graded on three elements — the number and complexity of problems addressed, the amount and complexity of data reviewed, and the risk of complications — as straightforward, low, moderate, or high. Code 99201 was deleted in 2021, which is why new-patient coding now starts at 99202. History and exam are still performed and documented, but they no longer set the level.

Other E/M subsections

Beyond office visits, E/M includes hospital inpatient and observation care, emergency department services, consultations, nursing-facility care, and preventive-medicine visits. Many of these were realigned in 2023 to follow the same time-or-MDM logic, but the office-visit rule is the one CBCS candidates must know cold.

Symbols and special code types

The CPT book uses symbols before codes to flag their status, and the exam expects you to recognize them:

• A filled circle marks a brand-new code for the current year, and a filled triangle marks a code whose descriptor was revised.
• A plus sign (+) marks an add-on code — a code that reports an additional service, can never stand alone, is always reported with a primary procedure, and is exempt from modifier -51.
• A circle with a slash marks a code that is exempt from modifier -51.

When no existing code accurately describes a service, the coder reports an unlisted procedure code and submits supporting documentation so the payer can determine a fee.

Coder workflow

To assign a CPT code, first look up the service in the alphabetic index (by procedure, organ, condition, or eponym), then verify the code in the numeric main text, reading every guideline and parenthetical note in that section. Never code straight from the index, because the index only points toward a range — the descriptor in the main text confirms the exact code. Check whether a modifier is needed, confirm the payer accepts the code, and pair it with a supporting ICD-10-CM diagnosis so the claim demonstrates medical necessity. Finally, verify the code is still valid for the current year, since a code correct last year may have been deleted on January 1.