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Stroke

The Elixhauser Index for comorbidity adjustment of in-hospital case fatality

From the Calgary Stroke Program, Department of Clinical Neurosciences, University of Calgary, AB, Canada.

Address correspondence and reprint requests to Dr. Michael D. Hill, Department of Clinical Neurosciences, University of Calgary, Foothills Hospital, Rm 1242A, 1403 29th Street NW, Calgary, Alberta, Canada T2N 2T9 michael.hill{at}calgaryhealthregion.ca

Background: Adjustment for comorbidity is an important component of any clinical outcome study using administrative data. The Elixhauser Index is a relatively newer comorbidity index for use with administrative data and has not been used to assess prognosis in patients with stroke. Similarly, an International Classification of Diseases (ICD)-10 coding algorithm has been rarely reported for Elixhauser Index.

Objective: To evaluate whether the Elixhauser Index provides a useful comorbidity adjustment for predicting in-hospital case-fatality in stroke outcome studies and to compare the degree of consistency using ICD-9-CM and ICD-10 coding algorithms.

Methods: Patients who had stroke from 1998 to 2000 (cohort A in the ICD-9-CM data) and 2003 to 2005 (cohort B in the ICD-10 data) in a large Canadian city were identified from the Hospital Discharge database. The performance of two coding algorithms for predicting the in-hospital case-fatality was assessed using multivariable logistic regression models. The C-statistic was used to compare the performance of each coding algorithm in predicting in-hospital case-fatality.

Results: Among 2,465 patients with stroke in the ICD-9-CM data (cohort A) and 2,987 patients with stroke in the ICD-10 data (cohort B), there was no difference in model performance using ICD-9-CM (C-statistic was 0.717) as compared with ICD-10 coding algorithms (C-statistic was 0.721; p = 0.83). Elixhauser comorbidity adjustment provided a better prediction of in-hospital case-fatality compared to reduced models including only age and gender (p < 0.0001) for both coding models.

Conclusion: The Elixhauser Index provides similar comorbidity adjusted risk estimates using both ICD-9-CM and ICD-10, and may be useful for predicting risk-adjusted in-hospital case-fatality in stroke outcome studies.

Abbreviations: ICD = International Classification of Diseases; ROC = receiver operator characteristic.

Supplemental data at www.neurology.org

Dr. Michael D. Hill is supported by a Health Scholar Award from the Alberta Heritage Foundation for Medical Research and by the Heart & Stroke Foundation Alberta/NWT/NU Professorship in Stroke Research.

Disclosure: The authors report no disclosures.

Received August 21, 2007. Accepted in final form April 21, 2008.

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