The mappings from ICD-9 to ICD-10 will be so critical to the conversion that a successful outcome depends on them being handled properly.

With that in mind, CMS along with the CDC unwrapped General Equivalence Mappings, GEMs for short. In the March issue of the Journal of AHIMA, the group described GEMs as “a translation dictionary to bridge the language gap between ICD-9-CM and ICD-10-CM/PCS.”

GEMs help users analyze and manage the code translation from ICD-9 to ICD-10, AHIMA explained, and ultimately build their own mappings as needed. That last bit is where the ICD-10 plot thickens. 

“A single one-size fits all map might seem like a reasonable solution; however, such a map would mean the code sets were so similar that there would be no point in transitioning to ICD-10-CM/PCS. The correlation of specificity and meaning between the two code sets is not that simple,” AHIMA states in the online version of its March 2010 practice brief Putting the ICD-10-CM/PCS GEMs into Practice.

[Related: Rising health IT budgets a boon to ICD-10.]

The practice brief includes segments on how to choose which GEM to use, what healthcare IT pros should not do with GEMs, direct conversion of applications, principals for developing applied mappings, and public domain reimbursement mappings. 

“Due to the differences in the ICD-9-CM and ICD-10-CM/PCS code sets and the multiple types of applications where coded data are used, applied maps based on the GEMs are the closest to an industry-wide consistent mapping standard that is likely to be reasonable and achievable,” AHIMA pointed out. “Although the differences in the code sets inherently present challenges to data comparability across the transition period, the development of applied mappings does not in and of itself add to these challenges as long as applied mappings are developed appropriately.”