Web Extra

Ann Zeisset

The transition to new code sets means that data encoded in either the old (ICD-9-CM) or new (ICD-10-CM/PCS) code sets will need to be converted or translated to the other code set to preserve the informational value of healthcare data. Maps are an integral component of this data conversion or translation process.

The Centers for Medicare & Medicaid Services (CMS) and the Centers for Disease Control and Prevention created the general equivalence mappings (GEMs) to ensure consistent national data when the United States makes the transition. The GEMs are a bidirectional translation tool that make it possible to accurately and effectively translate between ICD-9-CM and ICD-10-CM/PCS coded data for a number of purposes, including:

  • Comparing data across the transition period for various purposes, such as long-term clinical studies, epidemiological and other research, and calculating costs and other institutional financial measurements
  • Financial modeling
  • Facilitating the conversion or refinement of ICD-9-CM-based applications, such as payment and coverage edits and policies, utilization/case management software, clinical risk grouping applications, quality measures, and groupers used for reimbursement and pricing

The GEMs are more complex than a simple one-to-one crosswalk. They reflect the relative complexity of the code sets clearly so that applications that use them can be managed effectively.

The GEMs organize the differences in the ICD-9-CM and ICD-10-CM/PCS code sets by linking a code in the "source" code set to all plausible translation alternatives in the "target" code set. Choices among the alternatives can be made depending on the particular conversion project for which the GEMs are being used. This refinement in code choices in the target code set is sometimes referred to as "applied mapping" and allows the possible choices in the target code set to be narrowed by implementing a set of user-defined criteria based on the specific purpose for which the map is being used (for example, the translation choices selected from among all of the given alternatives might be different for a reimbursement mapping project than for a clinical research study).

The GEMs are intended to be used by anyone who needs to convert coded data or convert software applications that produce or process coded data from ICD-9-CM to ICD-10-CM/PCS. They can also be used to translate incoming ICD-10-CM/PCS data back to ICD-9-CM after the implementation date. Not all ICD-10-CM/PCS conversion projects will need to use the GEMs. When a small number of ICD-9-CM codes is being converted to ICD-10-CM/PCS, it may be quicker, easier, and more accurate to simply look up the correct codes.

It is inappropriate to use the GEMs as a substitute for learning how to use the ICD-10-CM/PCS code sets. Mapping simply links concepts in the two code sets, without consideration of context or specific patient encounter information, whereas coding involves assigning the most appropriate code based on health record documentation and applicable coding rules and guidelines. When coding health records, codes should be assigned using an ICD-10-CM/PCS code book or coding software and should be based on health record documentation.

For more information, see Ann Zeisset and Sue Bowman's "Strategies for ICD-10 Implementation", hfm, September 2012


Publication Date: Monday, September 03, 2012

Login Required

If you are an existing member, please log in below. Username and password are required.



Forgot User Name?
Forgot Password?

If you are not an HFMA member and would like to access portions of our content for 30 days, please fill out the following.

First Name:

Last Name:


   Become an HFMA member instead