Health Information Management

Tip: Using CMS’ ICD-10 General Equivalence Mappings

APCs Insider, December 19, 2014

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The General Equivalence Mappings (GEMs) that are publicly available on CMS' website were developed by CMS and the CDC, along with representatives from the American Hospital Association and AHIMA.
Using the GEMs, HIM professionals can map ICD-9-CM to ICD-10-CM/PCS codes—known as forward mapping—and ICD-10-CM/PCS codes to ICD-9-CM—known as backward mapping. Collectively, four separate files make up the GEMS:
  • ICD-9-CM diagnosis codes to ICD-10-CM
  • ICD-9-CM procedure codes to ICD-10-PCS
  • ICD-10-CM to ICD-9-CM diagnosis codes
  • ICD-10-PCS to ICD-9-CM procedure codes
However, the GEMs were not created as a replacement for coding natively in ICD-10. According to the AHIMA practice brief, "Putting the ICD-10-CM/PCS GEMs Into Practice," CMS created the public domain GEMs to:
  • Convert large databases and create data sets to test systems and applications
  • Link data in long-term clinical studies
  • Develop application-specific mappings
  • Analyze data collected before and after the transition to ICD-10-CM/PCS
CMS updates the GEMs annually, though they have remained relatively stable in recent years due to the extended code freezes for ICD-9-CM and ICD-10.
The Cooperating Parties made the last regular update to either code set October 1, 2011. Subsequent annual updates have been limited to new technologies and diseases. The first regular update to ICD-10 is scheduled for one year after implementation, while ICD-9-CM will see no further updates. CMS intends to continue updating the GEMs for three years after ICD-10 implementation.
This tip is adapted from “Providers lagging in ICD-10 training should not be tempted to rely on GEMs” in the December issue of Briefings on APCs.

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