General Equivalence Mappings (GEMs) were the creation of work completed by the National Center for Health Statistics (NCHS), CMS, the American Health Information Management Association, the American Hospital Association, and 3M Health Information Systems in an attempt to convert codes between ICD-9 and ICD-10. Most recently, NCHS published the translation dictionary for diagnoses. Similarly, CMS published a translation dictionary for procedures. Collectively, these are called GEMs. This effort created a national version to ensure consistency in national data.
GEMs can be thought of as two-way translation dictionaries, in which diagnoses and procedure codes can be translated to and from ICD-9-CM and ICD-10-CM/ICD-10-PCS. The translations go in both directions so that it is possible to look up a code to find out what it means according to the concept and structure used by the other coding system. The forward and backward mapping GEMs aren’t mirror images of each other because the translation alternatives are based on the meaning of the code you are looking up.
The GEMS are set up as “flat files,”which are data files that contain records with no structural relationships. Unless you are very tech savvy, they are difficult to work with. However, the American Academy of Professional Coders (AAPC) has developed the Code Translator tool, which takes these files and very simply allows you to map both forward and backward from ICD-9-CM and ICD-10-CM, meaning this conversion tool allows you to convert ICD-9 codes to ICD-10 codes or vice versa. The tool is free, and you don’t have to be an AAPC member to use it.
Take care with how you use the Code Translator or the GEMs. While the mapping is great to help you narrow down your search, it cannot be used without a coding book, which you should consult to confirm codes. In many instances, a particular ICD-9-CM code may map to several ICD-10-CM code choices, requiring you to narrow down and sort through the results. Also, with the abundance of ICD-10-CM codes, there are many that just don’t map from ICD-9-CM codes.
The files are great for working with physicians to help them determine which codes to migrate to from ICD-9-CM to ICD-10-CM. The GEMs also help take the chore out of looking up multiple variables until you become more familiar with the new code system. Keep in mind to check the new guidelines whenever mapping any codes.