Pair Up Allowable Add-on and Primary Codes

CMS quick reference tool makes it easy to make the right choice.

By G.J. Verhovshek, MA, CPC

Identifying exactly which primary code(s) may be reported with a particular add-on code is a persistent problem coders often encounter. Add-on codes may be listed in proximity to the primary codes they accompany, and/or CPT® may provide explicit instruction (e.g., “Use 64148 in conjunction with 36147”), but not always. A change to the CMS Manual System released earlier this year, however, provides a handy reference to help you quickly identify allowable add-on and primary code pairs.

Rules Governing Add-on Codes

Be familiar with “add-on” codes and the rules that govern their use. Specifically:

  • Add-on codes describe procedures or services that are always provided “in addition to” other related services or procedures. Add-on codes cannot stand alone as separately reportable services.
  • Add-on codes are identified throughout the CPT® codebook by a “+,” and their descriptor will contain some variation of the phrase “report in addition to code for primary procedure.” You can find a complete list of add-on codes in Appendix D of the CPT® codebook.
  • Add-on codes have no global period assigned; they are included in the global surgical fee for the primary procedure.
  • Add-on codes are modifier 51 exempt, and are to be paid at full fee schedule value. Their assigned value accounts for the additional nature of the procedure.

Three Kinds to Classify

The Centers for Medicare & Medicaid Services (CMS) transmittal 2636 (change request 7501, Jan. 16, 2013) classifies add-on codes into one of three types:

Type I – This type of add-on code has a limited number of identifiable primary procedure codes.

Type II – These add-on codes do not have a specific list of primary procedure codes. CMS encourages claims processing contractors to develop their own lists of allowable code pairs.

Type III – The CPT® codebook is inconsistent in how it identifies primary codes for this type of add-on code. CMS advises claims processing contractors to develop their own lists of allowable primary codes for these add-on codes.

Quickly Match the Type I and Primary Codes

CMS lists in the transmittal each add-on CPT® code and identifies it as either Type I, Type II, or Type III. For those add-ons identified as Type I, CMS lists their acceptable primary procedure codes. Because the vast majority of add-on codes are classified as Type I, the transmittal provides a quick reference to find which add-on codes go with which primary procedure codes.

For example, CMS identifies the allowable primary procedures for +0159T Computer-aided detection, including computer algorithm analysis of MRI image data for lesion detection/characterization, pharmacokinetic analysis, with further physician review for interpretation, breast MRI (List separately in addition to code for primary procedure) to be 77058, 77059, C8903, C8904, C8905, C8906, C8907, and C8908. And one look at the list tells you the only allowable primary procedure with +67225 Destruction of localized lesion of choroid (eg, choroidal neovascularization); photodynamic therapy, second eye, at single session (List separately in addition to code for primary eye treatment) is 67221 Destruction of localized lesion of choroid (eg, choroidal neovascularization); photodynamic therapy (includes intravenous infusion).

Note: The code pairings in CMS transmittal 2636 are based on Medicare guidelines, not the American Medical Association’s (AMA). CMS instructions closely match those in the CPT® codebook, with a few exceptions. For example, CPT® allows separate reporting for use of an operating microscope (+69990 Microsurgical techniques, requiring use of operating microscope (List separately in addition to code for primary procedure)) with many dozens of codes from throughout the CPT® codebook (including Category III codes); whereas, CMS allows +69990 with relatively few codes from the 6xxxx series.

For the small number of Type II and Type III codes, you’ll have to rely on your individual payer for guidance. With your new quick reference tool, however, you can now quickly identify those codes.


G.J. Verhovshek, MA, CPC, is managing editor at AAPC.


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