|HCUP Methods Series Comorbidity Software Documentation|
Healthcare Cost and Utilization Project (HCUP)
Agency for Healthcare Research and Quality
For Technical Assistance with HCUP Products:
Recommended Citation: Elixhauser A, Steiner C, Kruzikas D.Comorbidity Software Documentation, January 2004. HCUP Method Series Report # 2004-01. ONLINE February 6, 2004. U.S. Agency for Healthcare Research and Quality.
Diagnoses and DRGs
The Comorbidity Software is a tool that assigns variables to identify comorbidities in hospital discharge records using diagnosis coding from the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM). This software, consisting of two computer programs, was developed at the Agency for Healthcare Research and Quality (AHRQ, formerly known as the Agency for Healthcare Policy and Research).
This document describes the software that maps ICD-9-CM diagnosis codes into comorbidity indicators, as reported by Elixhauser et al. (Comorbidity Measures for Use with Administrative Data. Medical Care, 1998;36:8-27). The report includes the technical documentation for the Comorbidity Software and describes three topics:
These programs will be useful to researchers and policy analysts seeking information on ways to assess and control for disease severity.
Comorbidity software assigns variables that identify comorbidities in hospital discharge records using the diagnosis coding of ICD-9-CM (International Classification of Diseases, Ninth Edition, Clinical Modifications). This document describes the software that creates the comorbidity measures reported by Elixhauser et al. ("Comorbidity Measures for Use with Administrative Data." Medical Care, 1998;36:8-27).
The comorbidity software consists of two SAS computer programs for PCs. Although these programs are written in SAS, they are being distributed in ASCII so that they can be readily adapted to other programming languages.
The first program, Creation of Format Library for Comorbidity Groups, creates a SAS format library that maps diagnosis codes into comorbidity indicators. Additional formats are created to exclude conditions that may be complications or that may be related to the principal diagnosis.
The second SAS program, Creation of Comorbidity Variables, applies these formats to a data set containing administrative data.
This document describes three topics:
|Data Elements and Coding Conventions
The input data file must contain certain elements that are coded in specific ways. These elements are required for the assignment of the comorbidity flags. The flags are 0/1 indicators that note whether individual records include each comorbidity.
The input data set must have the following two variables:
Required Elements of Input File
Creation of Format Library for Comorbidity Groups
The format program defines a format library that contains the diagnosis screens necessary for the comorbidity analysis. It will be used by Program 2, the comorbidity analysis program.
Creation of Comorbidity Variables
The analysis program assigns to the inpatient records 0/1 indicators for the comorbidity variables of interest. This program assumes that the input data file conforms to specific variables names, attributes, and coding conventions, as described above.
There is an options statement that defines page and line size preferences; the settings currently are linesize=159 and pagesize=56. These settings can be changed, depending upon whether you prefer portrait or landscape style output.
|Diagnoses and DRG´s|
ICD-9-CM and DRG coding changes through September 30, 2004, are incorporated into this software. Appendix 1 contains these coding changes.
Thirty comorbidity variables are created using the comorbidity software, based on the format library. The library contains formats for the ICD-9-CM codes and DRG screens. Construction of these variables is summarized in Appendix 2.
The original table appeared in the paper by Elixhauser et al (1998). This table has been updated to reflect the ICD-9-CM and DRG updates in the software.
The comorbidity program files can be downloaded from the HCUP-US website at:
Though they are written in SAS, both files are being distributed in ASCII so they can be readily adapted to other programming languages.
|Appendix 1. Changes Made to Comorbidity Software for FY2004, Version 2.0|
The following changes were made to the Comorbidity Software for fiscal year 2004. This year included not only ICD-9-CM updates for fiscal year 2004, but also some modifications to the software as described below. These changes are incorporated in the tool currently available: Comorbidity Software, Version 2.0.
|Appendix 2. Definitions of Comorbidity
|Note: A hierarchy was established between the following pairs of comorbidities: If both uncomplicated diabetes and complicated diabetes are present, count only complicated diabetes. If both solid tumor without metastasis and metastatic cancer are present, count only metastatic cancer.|
|Internet Citation: HCUP Comorbidity Software. Healthcare Cost and Utilization Project (HCUP). October 2015. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/reports/methods/2004_1.jsp.|
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