Easy GEM Based Mapper

Health Data Consulting is pleased to offer an easy GEM based mapping tool as an aid to the industry.    This tool is based on the CMS published 2014 GEM (General Equivalency Mapping) files for ICD-9 diagnosis and ICD-10-CM codes.  It is helpful in identifying sets of codes in ICD-10 that are included in the GEM mapping files.  GEM mapping does not consistently identify all of the codes that would meet the intent that the user initially had in an existing ICD-9 set and it may bring over codes that do not meet that initial intent as defined in ICD-9.  It is however a valuable help in starting the mapping process.
The process of identifying the ICD-10 codes that would represent the same intent as a current set of ICD-9 codes involves several steps when using GEM files.

  • Make sure that the intent of the current set of ICD-9 codes is correct and that the category (with the articulation of the concepts that should or should not  be included) is clearly defined.
  • Use GEM to map all of the ICD-10 codes to the set of ICD-9 codes in both directions ICD-9 to ICD-10 and ICD-10 to ICD-9.
  • Review the returned list of codes and query ICD-10 independently to see if there are codes that may have been left out based on the intent of the defined category.
  • Review the returned list of codes to see if codes were included in the GEM mapping that did not meet the intent of the defined category.
  • Save the thoroughly reviewed and edited list of ICD-10 codes in excel or some other format to represent the intent as defined in ICD-10 along with the attached definition for that code set for any intended analytic or  business use.

Using the mapping tool:

  • Take a list of ICD-9 codes (or ICD-10 codes depending on the direction) and copy and paste the list into the code list field “Paste Codes Here”.
  • Codes can be pasted from a list of codes in an excel spreadsheet or a text file of codes.
  • The tool will work with or without the decimal
  • Ranges, “short codes” or invalid codes will not be accepted
  • If the plan is to identify all potential codes in ICD-10 that would map to a list of existing ICD-9 codes:
    • Paste the list of 9 codes in the list field
    • Set the code type to ICD 9
    • Select Mapping type “bidirectional”
  • Selecting “Map Codes >>”  will display a list of unique ICD-10 codes (duplicates from mapping have been removed)
  • You can down load the list of codes and descriptions into an excel spreadsheet or CSV file and save the file on you local machine.  “Download to CSV File” or “Download to Excel File” at the bottom of the code list
  • Mapping can also be done from ICD-10 to ICD-9 and can be bi-directionally or in one direction.
  • Any mapping of groups of codes should be done directionally
  • Registration is required to gain access, but once registered, access is not limited.
  • Please contact joenichols@healthdataconsulting.com if there are any questions or suggestions.


HDC provides no guarantees of the accuracy of mapping based on this tool or the outcome of any mapping process using this tool.  It is intended as a free tool to use as one part of the investigation needed to identify the code set that meets each users intent.  The user is responsible for the results of the mapping process.

Click here to access the tool