Inpatient Facility Coding & Compliance Alert

Question: What is the difference between a cross walk and a GEM?

Texas Subscriber

Answer: Although most people tend to use these two terms interchangeably, there is a difference in between the two.

According to Procedure Code Set General Equivalence Mappings: ICD-10-PCS to ICD-9-CM and ICD-9-CM to ICD-10-PCS Documentation and User’s Guide, issued by CMS this April,

“The word ‘crosswalk’ is often used to refer to mappings between annual codes updates of I-9. Crosswalk carries with it a comfortable image: clean white lines mark the boundary on either side; the way across the street is the same in either direction; a traffic signal, or perhaps even a crossing guard, aids you from one side to the other. Please be advised: GEMs are not crosswalks. They are reference mappings, to help the user navigate the complexity of translating meaning from one code set to the other. They are tools to help the user understand, analyze, and make distinctions that manage the complexity, and to derive their own applied mappings if that is the goal.”

In fact, the GEMs are much more than a simple one-to-one crosswalk. They carry much more information that may be more useful. One entry in a GEM may map to its many possible counterparts in the other code system. They tend to reflect the relative complexity of the code sets.

Example: ICD-9 to PCS GEM: Single type entry for ICD-9 code 02.11

02.11 Simple suture of dura mater of brain maps to:

• 00Q20ZZ – Repair of dura mater, open approach
• 00Q23ZZ – Repair of dura mater, percutaneous approach 
• 00Q24ZZ – Repair of dura mater, percutaneous endoscopic approach.