Elixhauser Comorbidity Software Refined for ICD-10-CM

The Elixhauser Comorbidity Software Refined for ICD-10-CM is one in a family of databases and software tools developed as part of the Healthcare Cost and Utilization Project (HCUP), a Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality. HCUP databases, tools, and software inform decision making at the national, State, and community levels.

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The Elixhauser Comorbidity Software Refined for ICD-10-CM assigns data elements that identify different pre-existing conditions based on secondary diagnoses (i.e., comorbidities) listed on hospital administrative data. In health services research, it is often important to control for comorbidities that coexist at the time of the hospitalization or outpatient encounter, impact resource allocation (e.g., length of stay or charges), and possibly affect healthcare outcomes, such as in-hospital mortality. The Elixhauser Comorbidity Software Refined for ICD-10-CM is based on the International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) diagnosis codes with indicators whether the diagnoses were present on admission (POA).

The Elixhauser Comorbidity Software was originally developed using ICD-9-CM diagnosis codes and diagnosis-related groups (DRGs) to identify comorbidities reported on adult, nonmaternal inpatient discharge data.1 The software was translated into ICD-10-CM prior to the availability of ICD-10-CM-coded data and released as a beta version. Once ICD-10-CM-coded data became available, the beta version was evaluated by clinical experts. The recommended modifications (implemented in v2021.1) transition the software tool out of its beta status and into the Elixhauser Comorbidity Software Refined for ICD-10-CM.

The Elixhauser Comorbidity Software Refined for ICD-10-CM retains the same clinical intent of defining a comprehensive list of comorbidity measures for use with large administrative databases, however refinements were made to the clinical criteria used for identification of comorbidities and also with some of the comorbidity measures themselves. The number of comorbidity measures increases from 29 to 38 starting in v2021.1 with three measures added, five measures modified to create 12 more specific measures, and one measure discontinued. A subset of the comorbidity measures uses the POA indicators to determine whether the condition indicated by the secondary diagnosis arose prior to or during the hospital stay. The remaining comorbidity measures do not use POA indicators because the condition can be assumed to be pre-existing and not the result of hospital care (e.g., diabetes, AIDS).


1 Elixhauser, Anne, et al. Comorbidity Measures for Use with Administrative Data. Medical Care, vol. 36, no. 1, 1998, pp. 8-27 JSTOR, https://www.jstor.org/stable/3766985. Exit Disclaimer Accessed 5 Sept. 2020.
 
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The Elixhauser Comorbidity Indices were originally developed using ICD-9-CM diagnosis codes and adult, nonmaternal inpatient discharge data.2 The development of the ICD-10-CM version of the indices was consistent with the methodology used for the ICD-9-CM version of the tool but used more recent 2018 data.

The Elixhauser Comorbidity Indices Refined for ICD-10-CM is designed to predict two frequently reported health outcomes:
  • Risk of in-hospital mortality
  • Risk of 30-day, all-cause readmission
Each index is a separate composite score based on the 38 individual comorbidity measures. Using the indices can be preferable to the individual measures because they account for interaction between comorbidities and reduces the necessary degrees of freedom required for estimation—especially helpful when working with small sample sizes.


2 Moore BJ, White S, Washington R, Coenen N, Elixhauser A. Identifying Increased Risk of Readmission and In-hospital Mortality Using Hospital Administrative Data: The AHRQ Elixhauser Comorbidity Index. Med Care. 2017 Jul;55(7):698-705.
 
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The following table provides information on where to find the various resources available for the Elixhauser Comorbidity Software Refined for ICD-10-CM tool. The download section includes all of the referenced materials.

Descriptions Elixhauser Comorbidity Resource
Development of Elixhauser Comorbidity Software Refined for ICD-10-CM User Guide: Elixhauser Comorbidity Software Refined for ICD-10-CM, Description of the Elixhauser Comorbidity Software Refined and Appendix A
Mapping diagnosis codes with more than one comorbidity measure User Guide: Elixhauser Comorbidity Software Refined for ICD-10-CM, Mapping of ICD-10-CM Diagnosis Codes into More Than One Comorbidity Measure and Appendix C
ICD-10-CM coding guidelines that may impact the identification of comorbidities User Guide: Elixhauser Comorbidity Software Refined for ICD-10-CM, ICD-10-CM Coding Guidelines that May Impact the Identification of Comorbidities
Background on the Elixhauser Comorbidity Software Indices Refined for ICD-10-CM User Guide: Elixhauser Comorbidity Software Refined for ICD-10-CM, Appendix B
 
Technical guidance for applying the Elixhauser Comorbidity Software Refined for ICD-10-CM to administrative data Elixhauser Comorbidity Resource
System requirements User Guide: Elixhauser Comorbidity Software Refined for ICD-10-CM, Using the Downloadable Elixhauser Comorbidity Measure for ICD-10-CM Files, System Requirements
Input files User Guide: Elixhauser Comorbidity Software Refined for ICD-10-CM, Using the Downloadable Elixhauser Comorbidity Measure for ICD-10-CM Files, Downloadable Files
Running the SAS programs User Guide: Elixhauser Comorbidity Software Refined for ICD-10-CM, Using the Downloadable Elixhauser Comorbidity Measure for ICD-10-CM Files, Downloadable Files and Running the Three SAS Programs Included With the Elixhauser Comorbidity Software Refined for ICD-10-CM
 
Additional resources Elixhauser Comorbidity Resource
Searchable list of measures in the Elixhauser Comorbidity Software Refined for ICD-10-CM Elixhauser Comorbidity Software Refined for ICD-10-CM Reference File, tab Comorbidity Measures
Searchable log of changes across versions Elixhauser Comorbidity Software Refined for ICD-10-CM Change Log

 
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Data Elements Required to Assign Elixhauser Comorbidity Measures

The input dataset must contain an array of ICD-10-CM diagnosis without decimals to define the comorbidity measures. To determine the 18 comorbidity measures that depend on knowing if the diagnosis was present on admission (POA), the input dataset must include POA indicators. The 20 comorbidity measures that do not depend on POA indicators will always be assigned.

Data Element Name in Program Purpose How to Modify the Data Element Name Used in the Program Data Element Name in HCUP Databases
DX1-DXn where n is the dimension of the diagnosis array. The dimension of the array must be at least 2 because the comorbidity measures are specific to secondary diagnoses. Array of ICD-10-CM diagnoses (without decimals) used to assign comorbidity measures Specify prefix for DX array using macro statement %LET DXPREFIX= I10_DX1-I10DXn in all HCUP databases starting in data year 2016
YEAR Discharge year (format YYYY), which is required to check whether ICD-10-CM diagnosis code is exempt from POA reporting Not modifiable. Hard-coded into program. YEAR
DQTR Discharge quarter (values 1 for Jan-Mar, 2 for April-June, 3 for July-Sept, 4 for Oct-Dec), which is required to check whether the ICD-10-CM diagnosis code is exempt from POA reporting Not modifiable. Hard-coded into program. DQTR
Required to assign 18 of the comorbidity measures: POA1-POAn where n is the dimension of the array of indicators that the diagnosis is present on admission. The dimension of the array must be the same length as the diagnosis array. Array of POA indicators required to assign the comorbidity measures for which coding is sensitive to the diagnosis being present on admission Specify prefix for POA array using macro statement %LET POAPREFIX= DXPOA1-DXPOAn

Data Elements Required to Assign the Elixhauser Comorbidity Indices Refined for ICD-10-CM

To assign the indices, the input dataset must contain all 38 comorbidity measures. The indices are designed to use all 38 comorbidity measures which means the data must have included POA indicators when the comorbidity measures were assigned.
 
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The ZIP folder includes the SAS format library program, a SAS mapping program, a SAS index program, and all of the user documentation. At this time, the Elixhauser Comorbidity Software Refined for ICD-10-CM tool is only available as a SAS program.

Elixhauser Comorbidity Software Refined for ICD-10-CM v2022.1: Fiscal Year 2022, Released October 2021 - valid for ICD-10-CM diagnosis codes through September 2022
For convenience, the user documentation for the Elixhauser Comorbidity Software Refined for ICD-10-CM v2022.1 is also provided as separate documents:

 
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Copies of previous versions of the Elixhauser Comorbidity Software Refined tool and the beta versions for ICD-10-CM are available for users who need to replace or access the old programs and documentation.

 
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Questions regarding the Elixhauser Comorbidity Software Refined may be directed to HCUP User Support through the following channels:

 
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Internet Citation: Elixhauser Comorbidity Software Refined for ICD-10-CM Healthcare Cost and Utilization Project (HCUP). October 2021. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/toolssoftware/comorbidityicd10/comorbidity_icd10.jsp.
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Last modified 10/29/21