Add-on Codes

Add-on codes are specific types of HCPCS/CPT codes intended to describe services that can only be reported in conjunction with a primary procedure. They represent additional work performed during the primary procedure and cannot stand alone as the main service being billed. Add-on codes can be reimbursed when reported with the primary procedure code by the same practitioner.

Key points about AOCs include:

• Dependency on Primary Codes: AOCs are inherently linked to specific primary codes. They are designed to capture the additional effort or complexity involved in a service that comes as an extension of another procedure.
• Billing: AOCs must be reported on the same claim as the primary service. They are generally not reimbursed if submitted without an associated primary code, as they don't stand alone as independent services.
• Documentation: Proper documentation should support the use of both the primary and add-on codes, indicating the necessity and performance of the additional service.
• Examples: Some common areas where add-on codes are used include anesthesia, surgery, radiology, and laboratory testing, where additional tasks are frequently performed in conjunction with a main procedure.

For accurate billing and compliance, it is crucial to understand the guidelines and the specific primary procedures to which an AOC can be attached, as defined by the coding manuals or payer policies.

CMS categorizes add-on codes to specify the payment policies associated with each type. Here are the three types of AOCs as per CMS guidelines:

1. Type I Add-On Codes: These codes describe additional services that are inherently performed in conjunction with a primary service. They cannot be reported alone and must be billed with specific primary procedure codes.
2. Type II Add-On Codes: These codes can be reported with a broader range of primary procedure codes. While they still must be reported in conjunction with a primary code, they are not restricted to specific primary codes like Type I.
3. Type III Add-On Codes: These are less common and often denote complex procedures that have multiple steps or components. They may combine elements from the first two types but generally require specific guidance about their appropriate use.

Add-on codes may be identified in three ways:

1. The add-on code is listed as a Type 1, Type 2, or Type 3 add-on code as mentioned above.
2. In the Physician Fee Schedule Lookup Tool, add-on codes generally have a global surgery period of “ZZZ.”
3. In the current year CPT Manual, an add-on code is designated by the symbol “+.” The code descriptor of an add-on code generally includes phrases such as “each additional” or “List separately in addition to primary procedure.”

Understanding these classifications ensures proper billing and compliance with CMS payment policies. It's crucial to consult the Medicare Physician Fee Schedule and other CMS resources for specific guidance on which primary services each add-on code can be paired with.

The add-on code listing which includes the types and process for determination are available at Medicare National Correct Coding Initiative Add-on Code Edits.

Revised 5/27/2025