Translating ICD-9 Codes Into ICD-10

The transition to ICD-10 obviously has a significant impact on billing practices. You and your staff may want to identify frequently used ICD-9 codes are develop a “cheat sheet” for ICD-10. If your practice currently uses a superbill, be aware this will likely need significant revisions. There are 69,000 ICD-10 codes as opposed to 14,000 ICD-9 codes. As such, the superbill may become too cumbersome, which may call for the need to explore other billing methods. 

General Equivalence Mappings (GEMS) were developed over several years by the National Center for Health Statistics, Centers for Medicare and Medicaid Services, AHIMA, the American Hospital Association, and 3M Health Information Systems. GEMS provide a temporary mechanism to link ICD-9 to ICD-10 and vice versa. It is important to keep in mind that in most cases, there are not exact matches between ICD-9 and ICD-10. Per CMS, “The purpose of GEMS is to create a useful, practical code to code translation reference dictionary for both code sets, and to offer acceptable translation alternatives wherever possible.”

A good way to think of GEMS is as a foreign language dictionary, where, for instance, there is an English to Spanish translation in the front, and a Spanish to English translation in the back. However, if you have studied foreign languages, you will know that there is sometimes not an equivalent for a particular word or phrase.

Where Can I Access These Files?

General Equivalence Mappings can be found on the following websites:

How Do I Read the GEMS files?

The files provide an ICD-9 to ICD-10 translation and an ICD-10 to ICD-9 translation. This is known as forwards and backwards mappings. These files provide a guide of how ICD-9 code “translate” into ICD-10. However, it is important to remember that the majority of time, there is not an exact match.

Once you open the file, you will notice there are numbers in three columns:

ICD-9 CM Source Code ICD-10 CM Source Code Flags
1550 C222 10000
1550 C227 10000
1550 C228 10000
1551 C221 00000

As mentioned above, there is also an ICD-10 to ICD-9 code mapping available:

ICD-10 CM Source Code ICD-9 CM Source Code Flags
C222 1550 10000
C223 1550 10000
C224 1550 10000
C227 1550 10000


There are two types of flags: For the purposes of GEMS, 1 means the flag is on and 0 means it is off. The Flags are divided into the following five sections:

  • Approximate: The approximate flag identifies entries where the complete meaning of the source system code and that of the target system code are not considered equivalent. 1= The translation is an Approximate match; 0= The translation is an Identical match.
  • No Map: The no map flag distinguishes entries where the source system code has at least one translation from entries where the source system code has no target system translation.1= There is no plausible translation for the source system code; 0 = There is at least one plausible translation for the source system code.
  • Combination: The combination flag distinguishes entries where the source system code has a single (meaning non-combination) translation alternative(s) from entries where the source system has a combination alternative (s). 1= the code maps to more than one code; 0 = the code maps to a single code

The last two columns, Scenario (4) and Choice List (5) are used to further clarify the Combination column, as follows:

  • A source system combination code includes diagnostic conditions or procedures that require more than one separate code in the target system to convey the equivalent amount of information.
  • Choice lists (the fifth flag) are the method for the translation alternatives in a combination entry.

Using the example of the diagnosis malignant neoplasm of the head of the pancreas, here is how the flags are interpreted:

ICD-9CM Code Description ICD-9CM Code ICD-10CM Code Description ICD-10CM Approximate No Map Combination Scenario Choice List
Malignant neoplasm of pancreas; head of pancreas 157.0 Malignant neoplasm of head of pancreas C25.0 0 0 0 0 0

What is the Purpose of GEMS? 

According to the CMS document entitled General Equivalence Mappings: Frequently Asked Questions , "the GEMs are a tool that can be used to convert data from ICD-9-CM to ICD-10-CM and PCS and vice versa. Mapping from ICD-10-CM and PCS codes back to ICD-9-CM codes is referred to as backward mapping. Mapping from ICD-9-CM codes to ICD-10-CM and PCS codes is referred to as forward mapping. The GEMs are a comprehensive translation dictionary that can be used to accurately and effectively translate any ICD-9-CM-based data, including data for:

  • Tracking quality;
  • Recording morbidity/mortality;
  • Calculating reimbursement; or
  • Converting any ICD-9-CM-based application to ICD-10-CM/PCS."