ICD-10 Myth Buster: Do GEMs provide simple one-to-one Reimbursement Mappings?

NCHS and CMS have published General Equivalency Mappings (GEMs) as a translation reference between I-10 and I-9 diagnosis and procedure codes. These “one-to-one” mappings translate one I-10 code to either one I-9 code or one cluster of up to six ICD-9 codes. This is why the mappings are referred to as both one-to-one and one-to-many.

I-9 Code Clusters

In some cases it takes as many as six I-9 codes combined (clustered) to reproduce one I-10 code. According to CMS, “This is the case with I-9 principal procedure codes such as coronary angioplasty that require the use of ‘adjunct’ I-9 codes to provide additional detail.”

I-10 Procedure Corresponding I-9 Procedures
02733ZZ: Dilation of Coronary Artery, Four or More Sites, Percutaneous Approach 00.66: PTCA or coronary atherectomy
00.43: Procedure on four or more vessels

If the procedure was performed on four or more vessels, the “adjunct” 00.43 I-9 code must be applied in addition to 00.66 because some reimbursement systems may pay more for a procedure performed on four or more vessels.

I-9 Code Alternatives

According to CMS, “More than one I-9 code may be a valid translation of a given I-10 code. Which one of those I-9 codes is the most correct translation cannot be determined based on the meaning of the codes themselves.”

I-10 Procedure Corresponding I-9 Procedures
0LQ70ZZ: Repair Right Hand Tendon, Open Approach 83.61: Suture of tendon sheath
83.64: Other suture of tendon


ICD-10 Reimbursement Mapping*
Distribution of mappings to single I-9 codes and I-9 code clusters

Code set Mapped to single
I-9 code
Mapped to 2-code cluster Mapped to 3-code cluster Mapped to 4-code cluster Mapped to 5-code cluster Mapped to 6-code cluster Total
I-10 codes
ICD-10-CM (diagnosis) 65,767 3,302 26 6 0 0 69,101
ICD-10-PCS (procedure) 69,657 1,211 583 458 36 12 71,957

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*Download CMS’ ICD-10-CM/PCS to ICD-9-CM Reimbursement Mappings 2010 Version Documentation and User’s Guide