General Equivalence Mappings 2012

Diagnosis Code Set 

General Equivalence Mappings

2012 Version Documentation

Appendix A—File and Format Detail


ICD-9-CM to ICD-10-CM
General Equivalence Mapping (GEM)

FILE FORMAT

FIELD	POSITION	LENGTH	VALUE
ICD-9-CM Code [source]	1 – 5	5	Left justified, blank filled No decimal
Filler	6	1	Blank
ICD-10-CM Code [target]	7 – 13	7	All seven characters used, no decimal
Filler	14	1	Blank
Approximate [FLAG]	15	1	1 = Yes/On 0 = No/Off
No Map [FLAG]	16	1	1 = Yes/On 0 = No/Off
Combination [FLAG]	17	1	1 = Yes/On 0 = No/Off
Scenario	18	1	0 – 9
Choice list	19	1	0 – 9

ICD-10-CM to ICD-9-CM
General Equivalence Mapping (GEM)


FILE FORMAT

FIELD	POSITION	LENGTH	VALUE
ICD-10-CM Code [source]	1 – 7	7	Left justified, blank filled No decimal
Filler	8	1	Blank
ICD-9-CM Code [target]	9 – 13	5	All seven characters used, no decimal
Filler	14	1	Blank
Approximate [FLAG]	15	1	1 = Yes/On 0 = No/Off
No Map [FLAG]	16	1	1 = Yes/On 0 = No/Off
Combination [FLAG]	17	1	1 = Yes/On 0 = No/Off
Scenario	18	1	0 – 9
Choice list	19	1	0 – 9

Glossary

Approximate flag — attribute in a GEM that when turned on indicates that the entry is not considered equivalent

Applied mapping — distillation of a reference mapping to conform to the needs of a particular application (e.g., data quality, research)

Backward mapping — mapping that proceeds from a newer code set to an older code set

Cluster — in a combination entry, one instance where a code is chosen from each of the choice lists in the target system entry, that when combined satisfies the equivalent meaning of the corresponding code in the source system

Choice list — in a combination entry, 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

Combination flag — attribute in a GEM that when turned on indicates that more than one code in the target system is required to satisfy the full equivalent meaning of a code in the source system

Combination entry — an entry in a GEM for which a code in the source system must be linked to more than one code option in the target system to be a valid entry

Complete meaning [of a code] — all correctly coded conditions or procedures that would be classified to a code based on the code title, all associated tabular instructional notes, and all index references that refer to a code

Forward mapping — mapping that proceeds from an older code set to a newer code set

General Equivalence Map (GEM) — reference mapping that attempts to include all valid relationships between the codes in the ICD-9-CM diagnosis classification and the ICD-10-CM diagnosis classification

ICD-9-CM — International Classification of Diseases 9th Revision Clinical Modification (I-9)

ICD-10-CM — International Classification of Diseases 10th Revision Clinical Modification (I-10)

No map flag — attribute in a GEM that when turned on indicates that a code in the source system is not linked to any code in the target system

Reference mapping — mapping that includes all possible valid relationships between a source system and a target system


Reverse lookup — using a GEM by looking up a target system code to see all the codes in the source system that translate to it

Scenario — in a combination entry, a collection of codes from the target system containing the necessary codes that when combined as directed will satisfy the equivalent meaning of a code in the source system

Single entry — an entry in a GEM for which a code in the source system linked to one code option in the target system is a valid entry

Source system — code set of origin in the mapping; the set being mapped ‘from’

Target system — destination code set in the mapping; the set being mapped ‘to’

Step 3: REFINE

Step 3: REFINE

REFINE Select the row(s) of an entry that meet the requirements of the applied mapping.

What is the purpose of the applied mapping? Does the applied mapping require that the code in the source system be mapped to only one “best” alternative in the target system? Will the correct applied mapping vary depending on the documentation in the record?

Once the user has analyzed all rows for an entry in a GEM, it is possible to select the row or rows most appropriate to an applied mapping. We will use two different sample entries—one combination entry from the ICD-9 to ICD-10 GEM and one single entry from the ICD-10 to ICD-9 GEM—in order to discuss the process of refining an entry and deriving an applied mapping.

Sample Entry 1—ICD-9 to ICD-10 GEM
896.2 Traumatic amputation of foot (complete) (partial), bilateral, without mention of complication

ICD-9 Code	ICD-9 Description	ICD-10 Code	ICD-10 Description	Approximate [FLAG]	No Map [FLAG]	Combination [FLAG]	Scenario	Choice list
896.2	Traumatic amputation of foot (complete) (partial), bilateral, without mention of complication	S98.011A	Complete traumatic amputation of right foot at ankle level, initial encounter	1	0	1	1	1
896.2	Traumatic amputation of foot (complete) (partial), bilateral, without mention of complication	S98.012A	Partial traumatic amputation of left foot at ankle level, initial encounter	1	0	1	1	2
896.2	Traumatic amputation of foot (complete) (partial), bilateral, without mention of complication	S98.021A	Complete traumatic amputation of right foot at ankle level, initial encounter	1	0	1	1	1
896.2	Traumatic amputation of foot (complete) (partial), bilateral, without mention of complication	S98.022A	Partial traumatic amputation of left foot at ankle level, initial encounter	1	0	1	1	2

In this instance the ICD-9 code specifies that the traumatic amputation is bilateral but does not specify whether it is partial or complete. Since both types of information—left or right foot, and whether the amputation is partial or complete—are specified in separate codes in ICD-10, the entry in the ICD-9 to ICD-10 GEM is a combination entry. There are two choice lists in this entry, because two codes in ICD-10 are required to satisfy the equivalent meaning in the ICD-9 combination code. And because the injury can be partial on one side and complete on the other, both sides partial, or both sides complete, there are two choices in each choice list.

After collating the combination entries into their respective choice lists (there is only one scenario), the four valid clusters are:

ICD-9-CM Source	to	ICD-10-CM Target
896.2 Traumatic amputation of foot (complete) (partial), bilateral, without mention of complication	≈ ≈ ≈ ≈	S98.011A Complete traumatic amputation of right foot at ankle level AND S98.012A Complete traumatic amputation of left foot at ankle level
		OR
		S98.011A Complete traumatic amputation of right foot at ankle level AND S98.022A Partial traumatic amputation of left foot at ankle level
		OR
		S98.021A Partial traumatic amputation of right foot at ankle level AND S98.012A Complete traumatic amputation of left foot at ankle level
		OR
		S98.021A Partial traumatic amputation of right foot at ankle level AND S98.022A Partial traumatic amputation of left foot at ankle level

To refine this entry, first the user must decide whether or not it is possible to choose a single cluster—the correct combination of left and right, partial and complete—and if possible, whether or not it is necessary. This decision of course depends on the use of the mapping.

A health information professional or health statistics researcher who is converting a limited number of old ICD-9 records to ICD-10, and has access to the individual medical record, can make use of the increased specificity in ICD-10 codes to re-code the record directly in ICD-10. The user can simply refer to the original record to see the specific nature of the bilateral traumatic amputation and assign the correct pair of ICD-10 codes to the record.

However, a health statistics analyst or data modeler who is translating aggregate ICD-9 data forward to ICD-10, and has no access to individual medical records, cannot make use of the fine distinctions in ICD-10 since they are not present in the old data. In this case, choosing a single cluster that is the closest equivalent cannot be the goal. The user must choose an ICD-10 code or pair of codes to represent all the ICD-10 alternatives, and could choose to fashion a rule by which to map similar cases. Rules specific to the applied mapping would promote consistency and document the decisions made. For example, here the applied mapping could use only the partial traumatic amputation codes.


Sample Entry 2—ICD-10 to ICD-9 GEM:
G92 Toxic encephalopathy

ICD-10 Code	ICD-10 Description	ICD-9 Code	ICD-9 Description	Approximate [FLAG]	No Map [FLAG]	Combination [FLAG]
G92	Toxic encephalopathy	323.71	Toxic encephalitis and encephalomyelitis	1	0	0
G92	Toxic encephalopathy	323.72	Toxic myelitis	1	0	0
G92	Toxic encephalopathy	349.82	Toxic encephalopathy	1	0	0

This same method could be used to translate a record coded in ICD-10 back to ICD-9, and could then be processed by a legacy payment system for reimbursement. The approximate flag is on, indicating that the relationship between the code in the source system and the code in the target system is an approximate equivalent. The approximate flag is on for all three target system ICD-9 code translations of ICD-10 code G92, because the complete meaning of G92 Toxic encephalopathy— as encompassed by the tabular instruction and index entries that refer to G92—includes the clinical concepts toxic encephalitis and encephalomyelitis, toxic myelitis, and toxic encephalopathy specified in three separate ICD-9 diagnosis codes.

To choose among the alternatives in ICD-9 is not possible based on the meaning of the codes themselves. Because the applied mapping is intended to establish general rules for translation rather than deciding on a case-by-case basis, then a consistent method must be derived and documented for resolving the disparity in classification between the two systems. Depending on the applied mapping, the user may choose the closest matching code description or the most frequently recorded of the ICD-9 code alternatives based on ICD-9 data.

For example, for mapping research data on toxic encephalitis during a period that overlaps the use of both ICD-10 and ICD-9, a valid one-to-one mapping from G92 to 323.72 could be derived. But for patient records coded in ICD-10 and mapped internally to an ICD-9 based medical necessity edit system during the transition period, it would depend on the classification of the ICD-9 code alternatives in the edit system. If all three ICD-9 codes were included in the same edit grouping, a valid one-to-one applied mapping to any of the three ICD-9 mapping choices could be derived.

Section 2: How to Use GEM Files

Section 2—How to Use GEM Files

For ease of use, we recommend loading the GEM files into a database along with the code descriptions for both code sets. With roughly 85,000 codes and their descriptions in both code sets, a desktop database like MS Access is adequate.

A general process for using the GEMs consists of three basic steps. In most cases it is expected these steps will be performed by software designed to integrate the GEMs content and translate codes or lists of codes from I-9 to I-10 or vice versa. In that case that a small number of records need to be translated, and the user has access to the original medical record, it is more efficient and accurate to look the codes up directly in the respective ICD-9-CM or ICD-10-CM book.

The code we will use for purposes of demonstration is I-9 code 599.72, Microscopic hematuria.

I-9 to I-10 GEM:
599.72 Microscopic hematuria

The illustrations at left and below display the I-9 code 599.72 as it appears in the I-9 to I-10 GEM. At left is the entry in text file format with its adjacent GEM entries, and below is the same information as it would appear in a desktop database. Note that the codes do not contain decimals in the GEMs.

59972 R311 10000 59972 R312 10000 59981 N3641 00000 59982 N3642 00000 59983 N368 10000 59984 N368 00000 59989 N398 00000 5999 N369 10000 5999 N399 10000

The code in the source system is listed first, followed by the code in the target system. Here the source system is the I-9 code and the target system is the I-10 code. The final group of digits is used to indicate additional attributes for entries in the map. The first three digits are called flags. The last two digits are used in combination entries, and will be discussed later. The GEM entry contains a flag characterizing the degree of correspondence between codes in one row (“approximate” flag), a flag for codes with no correspondence in the target system (“no map” flag) and a flag indicating the row is part of a combination entry (“combination” flag). If the digit is 1, the flag applies (is “turned on”) to that entry in the GEM. If the digit is 0, the flag does not apply (is “turned off”) to that entry in the GEM. In other words, 1 means “yes,” the flag applies to the entry in a GEM and 0 means, “no,” the flag does not apply. There are two rows in the I-9 to I-10 GEM for code 599.72. The entry is of the single type, meaning that each row—code 599.72 linked to one of two I-10 code alternatives—is considered a valid entry.

I-9 Code	I-9 Description	I-10 Code	I-10 Description	Approximate [FLAG]	No Map [FLAG]	Combination [FLAG]
599.72	Microscopic hematuria	R31.1	Benign essential microscopic hematuria	1	0	0
599.72	Microscopic hematuria	R31.2	Other microscopic hematuria	1	0	0

Step 2: ANALYZE

Is the “approximate” flag turned on? If yes, the correspondence is not a precise equivalent. Is the “no map” flag turned on? If yes, there is no corresponding code in the target system. Is the “combination” flag turned on? If yes, more than one code is the target system is required to satisfy the meaning of the code in the source system.

In the GEMs, there are three flags:

Approximate	indicates that the entry is not considered equivalent
No Map	indicates that a code in the source system is not linked to any code in the target system
Combination	indicates that more than one code in the target system is required to satisfy the full equivalent meaning of a code in the source system

The Approximate Flag

I-9 Code	I-9 Description	I-10 Code	I-10 Description	Approximate [FLAG]	No Map [FLAG]	Combination [FLAG]
599.72	Microscopic hematuria	R31.1	Benign essential microscopic hematuria	1	0	0
599.72	Microscopic hematuria	R31.2	Other microscopic hematuria	1	0	0

The approximate flag is turned on when no one code in the target system or linked combination of codes in the target system expresses the same essential meaning as the code in the source system. The difference between the two systems is typically in level of detail between the codes, and in nearly all cases the I-10 code is more detailed than the I-9 code.

The approximate flag is on for both rows in the source system GEM entry for I-9 code 599.72. The level of detail differs here—the type of hematuria is specified in I-10 and not in I-9. Although 599.72 Microscopic hematuria in I-9 and R31.2 Other microscopic hematuria in I-10 could be said to be equal, in fact they are not, because the I-9 code represents all varieties of microscopic hematuria and the I-10 code represents only microscopic hematuria not classified in the other code. The approximate flag is turned on to indicate no single code in I-10 expresses the same meaning as 599.72.

The approximate flag is on for the majority of entries in the GEMs. This may include code pairs that have the same description in both code sets. In such cases, neighboring codes in a subcategory are more specific in one code set than another, and so the number of clinical conditions included in a code is different—hence it does not express the same essential meaning. Codes containing the word “other” in their description are a common example.

I-10 Code	I-10 Description	I-9 Code	I-9 Description	Approximate [FLAG]	No Map [FLAG]	Combination [FLAG]
B37.41	Candidal cystitis and urethritis	112.2	Candidiasis of other urogenital sites	1	0	0
B37.42	Candidal balanitis	112.2	Candidiasis of other urogenital sites	1	0	0
B37.49	Other urogenital candidiasis	112.2	Candidiasis of other urogenital sites	1	0	0

In this example, the body sites included in the “other candidiasis” code differs between code sets, so the approximate flag is on for all entries in this subcategory. I-10 has specific codes for cystitis/urethritis and balanitis. I-9 does not. In I-9, balanitis is listed as an “includes” note under the code 112.2 Candidiasis of other urogenital sites, and cystitis or urethritis have no specific entry in tabular.

The No Map Flag

I-9 Code	I-9 Description	I-10 Code	I-10 Description	Approximate [FLAG]	No Map [FLAG]	Combination [FLAG]
V64.41	Laparoscopic surgical procedure converted to open procedure	NoDx	No Description	0	1	0
V64.42	Thoracoscopic surgical procedure converted to open procedure	NoDx	No Description	0	1	0
V64.43	Arthroscopic surgical procedure converted to open procedure	NoDx	No Description	0	1	0

In the I-9 to I-10 GEM, the “no map” flag is on for a subset of I-9 codes. In this example, the I-9 codes do not identify a diagnosis, but instead further specify the reason why a procedure was performed differently than planned. The recommendation was made that I-10 diagnosis codes do not contain information regarding procedures, so I-10 does not contain an equivalent group of codes. Therefore, the I-9 codes cannot be linked to I-10 at all. In the I-9 to I-10 GEM they are listed without a corresponding I-10 entry, and with the “no map” flag on.

The Combination Flag

The combination flag is turned on when a code in the source system must be linked to more than one code in the target system to be a valid entry. When the combination flag is on, the scenario and choice list fields in a GEM file contain a number. They appear last in a GEM file, after the flags. These numbers allow the user to collate the combination entries in the GEM.

T422X1A 9662 10111 T422X1A E8558 10112 T422X1A 9660 10121 T422X1A E8558 10122 T422X1D V5889 10000 T422X1S 9090 10111 T422X1S E9292 10112 T422X2A 9662 10111 T422X2A E9504 10112 T422X2A 9660 10121 T422X2A E9504 10122 T422X2D V5889 10000 T422X2S 9090 10111 T422X2S E959 10112

I-10 to I-9 GEM:
T42.2X1A Poisoning by succinimides and oxazolidinediones, accidental (unintentional),initial encounter

The illustrations at left and below display the I-10 to I-9 GEM entry for I-10 diagnosis code T42.2X1A Poisoning by succinimides and oxazolidinediones, accidental (unintentional), initial encounter. At left is the entry in text file format, and below is the same information as it would appear in a desktop database. The I-10 combination code T42.2X1A specifies both the diagnosis and the external cause, so it requires a combination entry in the GEM. A combination entry is subdivided hierarchically on two levels: 1) By scenario, the number of variations of diagnosis combinations included in the source system code, and 2) By choice list, the possible target system codes that combined are one valid expression of a scenario.

Each of the two types of drug listed in the I-10 code T42.2X1A is a unique I-9 code, so there are two scenarios from which to choose an applied mapping: one that specifies poisoning by succinimides and one that specifies poisoning by oxazolidinediones. Because each drug type listed in the I-10 combination code requires its own diagnosis code in I-9, each variation of the diagnosis is assigned a separate scenario number in the GEM entry.

A scenario designates one variation of the meaning of the source system diagnosis as specified in a combination code. In other words, it identifies one roughly equivalent expression of the source system code. In this example, scenario 1 contains the I-9 codes needed to satisfy the equivalent meaning of “Poisoning by succinimides, accidental (unintentional), initial encounter” Scenario 2 contains all the I-9 codes needed to specify “Poisoning by oxazolidinediones, accidental (unintentional), initial encounter.”

A scenario is subdivided into two or more choice lists of codes in the target system. These are the codes that must be linked together as a unit in an applied mapping to satisfy the equivalent meaning of the combination code in the source system. A choice list contains one or more codes in the target system that express a portion of the meaning of the code in the source system. A code must be included from each choice list in a scenario to satisfy the equivalent meaning of the code in the source system.

Scenario 1

I-10 Code	I-10 Description	I-9 Code	I-9 Description	Approximate [FLAG]	Combination [FLAG]	Scenario	Choice list
T42.2X1A	Poisoning by succinimides and oxazolidinediones, accidental (unintentional), initial encounter	966.2	Poisoning by succinimides	1	1	1	1
T42.2X1A	Poisoning by succinimides and oxazolidinediones, accidental (unintentional), initial encounter	E855.8	Other specified drugs acting on central and autonomic nervous systems	1	1	1	2

Scenario 2

I-10 Code	I-10 Description	I-9 Code	I-9 Description	Approximate [FLAG]	Combination [FLAG]	Scenario	Choice list
T42.2X1A	Poisoning by succinimides and oxazolidinediones, accidental (unintentional), initial encounter	966.0	Poisoning by oxazolidine derivatives	1	1	2	1
T42.2X1A	Poisoning by succinimides and oxazolidinediones, accidental (unintentional), initial encounter	E855.8	Other specified drugs acting on central and autonomic nervous systems	1	1	2	2

In this example there are two I-9 choice lists in scenario 1 and two I-9 choice lists in scenario 2, with one I-9 code in each list.

This is a comparatively simple example of a combination entry because each choice list contains only one code. The user does not need to choose among alternatives beyond the scenario.

The result is that for this I-10 combination entry, there are only two applied mapping alternatives:

Scenario 1

ICD-10-CM Source	to	ICD-9-CM Target
T42.2X1A Poisoning by succinimides and oxazolidinediones, accidental (unintentional), initial encounter	≈	966.2 Poisoning by succinimides AND E855.8 Other specified drugs acting on central and autonomic nervous systems

OR


Scenario 2

ICD-10-CM Source	to	ICD-9-CM Target
T42.2X1A Poisoning by succinimides and oxazolidinediones, accidental (unintentional), initial encounter	≈	966.0 Poisoning by oxazolidine derivatives AND E855.8 Other specified drugs acting on central and autonomic nervous systems