Which type of codes can only be used if no Category I or Category III code is available?

Unlisted procedure codes are specifically designed to be utilized when there are no appropriate Category I or Category III codes available to describe a service or procedure. These codes provide the flexibility to report procedures that may not have a specific code, allowing healthcare providers to communicate the nature of the service rendered.

When there's an unusual or new procedure that does not fit within the existing coding categories, using an unlisted code helps ensure accurate billing and documentation. However, it is important to provide detailed information about the service when using an unlisted code, so payers understand the procedure performed.

Other types of codes, such as stand-alone codes, modifier codes, and indented codes, serve different purposes within the coding system. Stand-alone codes refer to those that describe a complete service or procedure on their own. Modifier codes are used to provide additional information about a service or procedure, often indicating that a service has been altered in some way, while indented codes are sub-categories that relate to a primary procedure but do not stand alone. None of these categories directly address the necessity of reporting when no specific code is available, making unlisted procedure codes the correct choice in this context.