CMS has developed coding edits in order to prevent improper payments. There are three different types of edits.

  1. Procedure to Procedure (PTP) edits prevent improper payment when incorrect code combinations are reported.
  2. Medically Unlikely Edits (MUE) are to prevent improper payments when services are reported with incorrect units of service.
  3. Add-on Code Edits list which primary codes may be used for each add-on code.
    • Type I add-on codes have a limited number of specifically defined primary procedure codes (defined either by the CPT® book, HCPCS manual, and/or CMS policy)
    • Type II codes do not have defined primary codes—each Medicare Administrative Contractor (MAC) creates its own list of primary codes
    • Type III codes—some primary codes are specifically identified, but MACs may develop additional primary codes

To learn more about NCCI edits, please visit