GEMs: Making This “True Crosswalk” Assumption Could Cost You Time and Money

Written by on March 2, 2012 in Features - No comments

By Suzanne Leder, BA, M. Phil, CPC, COBGC, certified AHIMA ICD-10 trainer

You have seen plenty of International Classification of Diseases, Ninth Revision (ICD-9) to International Classification of Diseases, 10th Revision (ICD-10) bridges online, but beware: these bridges are based on general equivalent mappings (GEM), which are only about 50 percent accurate. If you rely solely on this mapping tool, you are likely to miss important coding subtleties, which could land your claim in limbo. Follow this step-by-step explanation to master GEMs and what each digit really means.

Basics: The important term to remember in general equivalent mappings is “general.”

The GEMs are the raw material from which providers, health information vendors and payers can derive specific applied mappings to meet their needs. You can use GEMs to study the differences between ICD-9-Clinically Modified (CM) and ICD-10-CM/(Procedure Coding System (PCS). The GEM file is a “flat file,” meaning this is a record with no structural relationships. You can download it here: http://www.cms.gov/ICD10/11b1_2011_ICD10CM_and_GEMs.asp#TopOfPage

Are GEMs a true crosswalk?

The word “crosswalk” is often used to refer to code mappings (as in, data element mappings between two distinct data models: ICD-9 and ICD-10), but be advised: GEMs are not true 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 you understand, analyze and make distinctions that manage the complexity, and to derive their own applied mappings (if that’s your goal).

The GEMs are more complex than a simple one-to-one crosswalk, and some statistics say they’re only about 50 percent accurate. GEMs reflect the relative complexity of the code sets clearly. The relationship between them is not simple. GEMs effectively demonstrate this, rather than making the transition from the old to the new code system in an oversimplified way.

What are GEMs relationships like?

You can have a variety of different code relationships in the GEMs file. Here are a few:

  • Some codes have a one-to-one correlation. Code 003.21 (salmonella meningitis) in ICD-9 matches up to A02.21 (salmonella meningitis) in ICD-10-CM.
  • Some codes won’t match because of specificity. For instance, 649.53 (spotting complicating pregnancy) does not exactly equal O26.851 (spotting complicating pregnancy, first trimester). To arrive at the correct code in ICD-10-CM, you have to know the trimester.

Also, ICD-10-CM codes may combine multiple diagnoses or concepts, such as:

  • a chronic condition with acute manifestation (G40.911, epilepsy, unspecified, intractable, with status epilepticus);
  • two concurrent acute conditions (R65.21, severe sepsis with septic shock);
  • acute condition with external cause (T39.012A, poisoning by aspirin, intentional self-harm, initial encounter).

On the other hand, ICD-10-CM code Z72.3 (lack of physical exercise) doesn’t have an ICD-9 target at all. So given you can have varied code relationships between the old system and the new, that’s why you can’t count the GEMs file as being cut-and-dried.

What key terms should you know?

  • “Target system” means the destination code set. In other words, this is the set the GEM is mapping to.
  • “Source system” means the original code set. In other words, this is the set the GEM is mapping from.
  • “Forward mapping” is when you see your ICD-9-CM code targeting an ICD-10-CM code.
  • “Backward mapping” is when you see an ICD-10-CM code targeting an ICD-9-CM code.
  • “Reverse lookup” means that you’re using a GEM by looking at a target system code and examining the codes that translate to it

Make sure you pay attention to key terms so you can ace the quiz at the end of this article! Think you’re ready now? Click here to for the quiz PDF.

What is an Example of a GEM?

Let’s look at the file itself. Here’s an example of what your GEM file looks like.

62130   N8500   00000

In GEM terms, 62130 is your source (which is code 621.30 with your decimal applied); N8500 is your target; and 00000 represents your flags.

Translation: This means 621.30 (endometrial hyperplasia, unspecified) maps directly to N8500 (endometrial hyperplasia, unspecified).

How do you know this? Let’s focus on the flags, the “00000” number.

What Do the Flags Mean?

Each digit of the “00000” number represents five different flags.

Key: The “0” means off. The “1” means on.

These flags are:

  • first digit: approximate flag
  • second digit: no map flag
  • third digit: combination flag
  • forth digit: scenario flag
  • fifth digit: choice flag

Examine the Approximate Flag

“Approximate” is flag one, which is in column one of the flags. The majority of alternatives are considered an approximate match. “0” means the translation is an identical match. This is rare in the procedure GEMs but more common in the diagnosis GEMs. Remember this example?

62130   N8500   00000

The first flag is a “0,” meaning you already know that 621.30 has an identical match in N8500. On the other hand, check out this example:

K3189   5363   10000

K3189   5375   10000

K3189   53789   10000

The first flag is a “1,” implies that the complete meaning of the source code differs from the complete meaning of the target system code. In other words, K31.89 (other diseases of stomach and duodenum) includes the meanings of all three codes: 536.3 (gastroparesis), 537.5 (gastroptosis), and 537.89 (other specified disorders of stomach and duodenum). This isn’t a direct match; all of these meanings are approximate.

Find out what no map’ flag means

“No Map” is flag two, which is in column two of the flags. A “1” means there is no plausible translation for the source system code. A “0” means there is at least one plausible translation for the source code. Let’s refer back to our familiar example:

62130   N8500   00000

This means you have at least one plausible translation for the source code. Code 621.30 has a plausible translation in N8500. However, look at this example:

T500X6A   NODX   11000

Because you see a “1” as flag 2, you can see that T500X6A (underdosing of mineralocorticoids and their antagonists, initial encounter) has no plausible translation. The “NODX” means no description found.

Conquer the combination flag

“Combination” is flag three, the scenario and choice list flags. When you see a “0” in this position, as in our example, this means the code maps to a single code.

62130   N8500   00000

In other words, 621.30 only maps to N8500. On the other hand, when you see a “1” in this position, this means the code maps to more than “1” code. Look at this example:

I25111   41401   10111

I25111   4139   10112

See the “1” in the third digit? This means that I25.111 (atherosclerotic heart disease of native coronary artery with angina pectoris with documented spasm) maps to 414.01 (coronary atherosclerosis of native coronary artery) with 413.9 (other and unspecified angina pectoris). Remember the term “with,” means “associated with” or “due to.”

Figure out the scenario flag

Now that you have identified flags one through three, let’s examine flags four and five (or the fourth and fifth digits). Flags four and five clarify combination entries. For the scenario flag (forth digit), you’ll see “0” meaning off, or digits 1 through 9 meaning, “In a combo entry, this is a collection of codes from the target system containing the necessary codes that combined as directed will satisfy the equivalent meaning of a code in the source system.” Source: General Equivalence Mappings: Documentation for Technical Users. Download at: http://www.cdc.gov/nchs/icd/icd10cm.htm

Here’s our previous example:

62130   N8500   00000

The “0” turns the scenario column off, so you know that you don’t need to worry about this. But this won’t always be the case:

T422X1A   9662   10111

T422X1A   E8558   10112

T422X1A   9660    10121

T422X1A   E8551   10122

Notice how you have “1” and “2” in the fourth digit column. This breaks down these codes into two scenarios, as follows:

Scenario 1: Code (T42.2x1A, poisoning by succinimides and oxazolidinediones, accidental [unintentional], initial encounter) maps to 966.2 (poisoning by succinimides) with E855.8 (accidental poisoning by other specified drugs acting on central and autonomic nervous systems).

Scenario 2: Code T42.2x1A (poisoning by succinimides and oxazolidinediones, accidental [unintentional], initial encounter) maps to 966.0 (poisoning by oxazolidine derivatives) with E85.58 (accidental poisoning by other specified drugs acting on central and autonomic nervous systems).

Choice flag can be a challenge

Finally, in the choice column or fifth digit, you’ll see “0” meaning off or digits “1” through “9” meaning, “In a combination entry, this is a list of one or more codes in the target system from which one code must be chosen to satisfy the equivalent meaning of a code in the source system.”

Source: General Equivalence Mappings: Documentation for Technical Users. Download at: http://www.cdc.gov/nchs/icd/icd10cm.htm

Here’s our previous example:

62130   N8500   00000

Because the last digit is a “0,” this means the choice column is off. On the other hand, look at this backwards mapping example:

R6521   99592   10111

R6521   78552   10112

The last digits here are “1” and “2.” This means that ICD-10-CM code R65.21 (severe sepsis with septic shock) matches to both 995.92 (severe sepsis) and 785.52 (septic shock). The ICD-10-CM code combines them both.

What should you do with this GEMs knowledge?

You might be reading through the GEMs flags and thinking, this is a very cumbersome process. Software folks are doing it, so you may think you don’t have to learn about GEMs. But you may have to verify your software for accuracy and find inconsistencies.

Action step: Start with the top 25. Pull the most common diagnoses you use in your office, and look into your system to see if they map correctly from ICD-9-CM to ICD-10-CM. Then you can get your vendor to correct them. Remember, inaccurate coding will result in increased denials and delayed payments.

This was a broad overview of GEMs. If you want to learn more, download this PDF: “General Equivalence Mappings: Documentation for Technical Users” at: http://www.cdc.gov/nchs/icd/icd10cm.htm. Think you got it down? Take the quiz to see if you really understand GEMs.

Suzanne Leder, M.Phil., CPC, COBGC, certified AHIMA ICD-10 trainer
can answer your ICD-10 coding questions. In addition to being ICD-10 trainer certified by the American Health Information Management Association (AHIMA), Suzanne is a Certified Obstetrics Gynecology Coder (COBGCTM). She has been the Ob-gyn Coding Specialty Alert editor for six years and counting. During her coding writing career, she has covered cardiology, gastroenterology, neurology, neurosurgery, orthopedics, otolaryngology, and physical medicine and rehab. Suzanne has a bachelor of arts degree from North Carolina State University and an international Master’s degree (M. Phil) from Trinity College Dublin. She became a Certified Professional Coder® (CPC®) through the American Academy of Professional Coders (AAPC) in 2004.

 

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