ICD-9-CM code

Question: The information in the introductions to the General Equivalence Mappings (GEM) points out that, in some cases, there is a clear one-to-one match between an International Classification of Diseases, 9th Edition, Clinical Modification (ICD-9-CM) code and an International Classification of Diseases, 10th Edition (ICD-10)-CM or ICD-10-Procedure Coding System (PCS) code. However, one ICD-9-CM code often translates to several ICD-10-CM or ICD-10-PCS codes because of the nature of going from the more general ICD-9-CM to the more specific ICD-10. Please describe the methodology that was used to create the GEMs.
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Answer
In order to both create and maintain the GEMs, all reasonable code translation alternatives are included in its respective GEM, based on the complete meaning of the code being looked up. For example, for the ICD-9-CM to ICD-10-CM GEM, we look up an ICD-9-CM code and include all reasonable translation alternatives in that GEM based on the "complete meaning" of the ICD-9-CM code. The "complete meaning" of a code includes tabular instruction, index entries, guidelines, and applicable Coding Clinic advice.


There may be multiple translation alternatives for a source system code (the code being looked up), all of which are equally plausible. This is true of both the ICD-10 to ICD-9-CM GEMs and the ICD-9-CM to ICD-10 GEMs. When there is only one alternative in a GEM, we can say that we have a "one-to-one" translation. This is common in the ICD-10 to ICD-9-CM GEMs and does not necessarily mean the two codes are identical. Additional information about this subject can be found at http://www.cms.hhs.gov/ICD10/01m_2009_ICD10PCS.asp. On this page, select the file labeled "2009 Mapping - ICD-10-PCS to ICD-9-CM and ICD-9-CM to ICD-10-PCS; and User Guide, Reimbursement Guide, Diagnosis, and Procedures" to access the mapping files.