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What You Need to Know About the GEMs
Everyone has heard about the GEMs (General Equivalence Mappings) created by CMS to ease the transition from ICD-9-CM to ICD-10-CM, but has anyone looked at them or read the GEM User’s Guide? For those planning on using the GEMs to code in the ICD-10-CM world, let’s take a closer look.
First, CMS states in the GEM Documentation and User’s Guide that the “GEMs are the raw material from which providers, health information vendors, and payers can derive specific applied mapping to meet their needs.” They emphasize that the GEMs are not crosswalks from ICD-9-CM to ICD-10-CM codes, but rather they are “reference mappings” to help navigate the complexity of translating the meaning of one code set to the other. These translations do not necessarily provide an exact match. In many cases there are multiple codes in the ICD-10-CM code set where only one single code exists in the ICD-9-CM code set. In other instances there is no code in ICD-10-CM for a specific ICD-9-CM code. This means that assigning the appropriate code is more than just selecting a code listed in the GEM.
CMS has created two sets of GEMs; one lists all the available ICD-9-CM codes and only the ICD-10-CM codes that are possible translations. This also called “forward mapping.” The other lists every ICD-10-CM code but only those ICD-9-CM codes that are plausible translations. This is called “backward mapping.” Together these GEMs provide a many-to-many mapping that that would make relying on them for day-to-day coding impossible and could even cause inaccurate reporting of diagnosis codes.
Let’s look at an example. The diagnosis of subarachnoid hemorrhage has only one code in the current ICD-9-CM code set, 430. The ICD-10-CM code set provides individual codes for the right and left carotid, MCA, ACA, PCA, and vertebral arteries, as well as codes for other and unspecified arteries. When we look up subarachnoid hemorrhage in the ICD-9-CM to ICD-10-CM GEM, code 430 is mapped to code I60.9 subarachnoid hemorrhage unspecified. If the patient’s medical record contains documentation regarding the specific artery responsible for the hemorrhage, assigning the unspecified code would be incorrect. This is only one example; there are many instances where the GEMs are mapped to unspecified codes when specific codes exist.
In the GEM User’s Guide CMS recommends coding directly from the ICD-9-CM or ICD-10-CM book when the coder has access to the medical record. With this in mind, you might ask why then did they create the GEMs? The answer is that they needed a method to process claims received with ICD-10-CM codes during the transition period to allow time for updating of medical policies and claims logic. Once ICD-10-CM is implemented, for a period of time CMS will take claims received and use the GEMs to translate the ICD-10-CM code to an ICD-9-CM code and then process the claim for payment. With this in mind, the true value of the GEMs for providers may be in determining the diagnosis code CMS used while processing their claim.
Author: Jenny Studdard, RCC, CPC, CPCO, AHIMA-approved ICD-10-CM Trainer