Monday, June 18, 2012


The Centers for Medicare & Medicaid Services (CMS) and the Centers for Disease Control and Prevention (CDC) created the national version of the General Equivalence Mappings (GEM) to ensure that consistency in national data is maintained. They have made a commitment to update the GEMs annually along with the updates to International Classification of Diseases, 10th Edition, Clinical Modification (ICD-10-CM) and Procedure Coding System (PCS) during the transition period prior to ICD-10 implementation. CMS and CDC will maintain the GEMs for at least three years beyond October 1, 2013, which is the compliance date for implementation of ICD-10 for all covered entities.

1. Are the General Equivalence Mappings a Substitute for Learning to Use the ICD-10-CM and ICD-10-PCS?
The GEMs are not a substitute for learning how to use the ICD-10-CM and ICD-10-PCS. Providers’ coding staff will assign codes describing the patients’ encounters from the ICD-10-CM and ICD-10-PCS code books or encoder systems. In coding individual claims, it will be more efficient and accurate to work from the medical record documentation and then select the appropriate code(s) from the coding book or encoder system. The GEMs are a tool to assist with converting larger International Classification of Diseases, 9th Edition, Clinical Modification (ICD-9-CM) databases to ICD-10-CM and ICD-10-PCS.

2. Who Can Use the General Equivalence Mappings?
The GEMs can be used by anyone who wants to convert coded data. Possible users of the GEMs include the following:

  • All payers;
  • All providers;
  • Medical researchers;
  • Informatics professionals; 
  • Coding professionals—to convert large data sets;
  • Software vendors—to use within their own products;
  • Organizations—to make mappings that suit their internal purposes or that are based on their own historical data; and 
  • Others who use coded data.

3. What are the General Equivalence Mappings?
The GEMs are a tool that can be used to convert data from ICD-9-CM to ICD-10-CM and PCS and vice versa. Mapping from ICD-10-CM and PCS codes back to ICD-9-CM codes is referred to as backward mapping. Mapping from ICD-9-CM codes to ICD-10-CM and PCS codes is referred to as forward mapping. The GEMs are a comprehensive translation dictionary that can be used to accurately and effectively translate any ICD-9-CM-based data, including data for:

  • Tracking quality; 
  • Recording morbidity/mortality;
  • Calculating reimbursement; or
  • Converting any ICD-9-CM-based application to ICD-10-CM/PCS.

The GEMs are complete in their description of all the mapping possibilities as well as when there are new concepts in ICD-10 that are not found in ICD-9-CM. All ICD-9-CM codes and all ICD-10-CM/PCS codes are included in the collective GEMs:

  • All ICD-10-CM codes are in the ICD-10-CM to ICD-9-CM GEM; 
  • All ICD-9-CM Diagnosis Codes are in the ICD-9-CM to ICD-10-CM GEM;
  • All ICD-10-PCS codes are in the ICD-10-PCS to ICD-9-CM GEM; and
  • All ICD-9-CM Procedure Codes are in the ICD-9-CM to ICD-10-PCS GEM.

4. How Have the General Equivalence Mappings Been Used to Date?
To date, the GEMs have been used to:

  • Translate ICD-9-CM codes in the Official ICD-9-CM Coding Guidelines to aid in producing the Official ICD-10-CM Coding Guidelines; 
  • Convert version 26.0 of Medicare Severity Diagnosis Related Groups from an ICD-9-CM-based application to an ICD-10-CM/PCS-based application;
  • Convert the Medicare Code Editor to a native ICD-10-CM/PCS-based application; and
  • Produce a purpose-built ICD-10-CM/PCS to ICD-9-CM crosswalk for reimbursement called the ICD-10 Reimbursement Mappings.

5. What are the Reimbursement Mappings?
The Reimbursement Mappings were developed by CMS in response to non-Medicare industry requests for a “standard one-to-one reimbursement crosswalk,” which is a temporary mechanism for mapping ICD-10-CM/PCS codes submitted on or after October 1, 2013 back to “reimbursement equivalent” ICD-9-CM codes. In order to develop the Reimbursement Mappings, CMS used the GEMs as a starting point by selecting the best ICD-9-CM code that maps to each ICD-10 code based on Medicare data. The Reimbursement Mappings identify the best matching ICD-9-CM code that can be used for reimbursement purposes for each ICD-10 code. All ICD-10-CM/PCS codes are in the Reimbursement Mappings; however, all ICD-9-CM codes are not in the Reimbursement Mappings. Where an ICD-10-CM/PCS code translates to more than one ICD-9-CM code, a single choice is required to create a functioning crosswalk. Inpatient hospital frequency data was used to aid in choosing a final ICD-9-CM translation in the crosswalk. If needed, the Reimbursement Mappings may be used to process ICD-10-CM/PCS-based claims received on or after October 1, 2013, with a legacy ICD-9-CM-based system as part of a planned transition period, until systems and processes are developed to process ICD-10-CM/PCS-based claims directly. The Reimbursement Mappings consist of two crosswalks:

  • ICD-10-CM to ICD-9-CM for Diagnosis Codes; and
  • ICD-10-PCS to ICD-9-CM for Procedure Codes.

CMS is not using the ICD-10 Reimbursement Mappings for any purpose. We are converting our systems and applications to accept ICD-10-CM/PCS codes directly.

6. Is There a One-to-One Match Between ICD-9-CM and ICD-10?
No, there is not a one-to-one match between ICD-9-CM and ICD-10, for which there are a
variety of reasons including:

  • There are new concepts in ICD-10 that are not present in ICD-9-CM;
  • For a small number of codes, there is no matching code in the GEMs;
  • There may be multiple ICD-9-CM codes for a single ICD-10 code; and 
  • There may be multiple ICD-10 codes for a single ICD-9-CM code.

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