Diagnosis classification GEMs

The Center for Medicare and Medicaid Services (CMS) is sponsoring a conference call to discuss "ICD-10-CM/PCS Implementation and General Equivalence Mappings (Crosswalks)".

The purpose of the call is to discuss "...the General Equivalence Mappings that have been created to assist in converting policies, edits, and trend data from ICD-9-CM to ICD-10-CM/PCS."

In other words, to help the switch to ICD-10-CM from ICD-9-CM go more smoothly, CMS is betting on "General Equivalence Mappings" to help people convert their ICD-9-CM encoded data to ICD-10-CM encoded data. A transition plan might therefore involve continuing to code with ICD-9-CM and then converting those codes to ICD-10-CM. (!)

Sounds easy, right?

That is doubtful.

First, we want to point out the irony of this policy. We were told over and over that we'd get better data from ICD-10-CM coding and the sooner the better. Now, we're being told we can continue coding along merrily in ICD-9-CM and just convert our data to ICD-10-CM afterwards. How could that possibly result in better data?

Furthermore, to use the General Equivalence Mappings (or GEMs), you need to know the following facts, taken from the materials CMS posted for the conference call:

- ICD-9 and ICD-10 codes are quite different

- One ICD-9 Diagnosis Code may be represented by multiple ICD-10 codes

- One ICD-10 Diagnosis Code may be represented by multiple ICD-9 codes

- A few ICD-10 codes have no predecessor ICD-9 codes

- Some payers found GEM detail daunting, therefore they developed a "reimbursement mapping" which is much simpler. It is not clear when to use this mapping vs. GEMs.

- There may be multiple translation alternatives for a source system code (the code being looked up), all of which are equally plausible. This is true of both the ICD-10 to ICD-9-CM GEMs and the ICD-9-CM to ICD-10 GEMs.

- A one-to-one mapping does not imply that the two codes refer to the same disease!

- There are instances where there is not a mapping between an ICD-9-CM code and an ICD-10 code. In these instances, CMS has flagged the code with a "no map" flag.

- Each GEM has FIVE flags:
        1. The "approximate" flag
        2. The "no map" flag
        3. A flag to indicate a one-to-many mapping
        4. and 5. Two flags to "further clarify one-to-many mappings".

- CMS et al. developed GEMs "...independently without reference to Medicare data."

- The ultimate goal of the GEMs, and the primary basis on which they are maintained and evaluated, is whether a given patient record receives the SAME Medicare Severity Diagnosis Related Group. Essentially, this means that the improved diagnostic precision of ICD-10-CM is irrelevant to how Medicare will reimburse hospital stays.

- The net effect of the switch and the GEMs on "trend data" (for example, the incidence of hypertension or type 2 diabetes mellitus over time) is not known, and CMS will monitor the effect after the switch.

Why are we switching again?