Charlson Index comorbidity adjustment for ischemic stroke outcome studies

Background and Purpose - The Charlson Index is commonly used in outcome studies to adjust for patient comorbid conditions, but has not been specifically validated for use in studies of ischemic stroke. The purpose of the present study was to determine whether outcomes of ischemic stroke patients varied on the basis of the Charlson Index. Methods - The Department of Veterans Affairs (VA) Stroke Study prospectively identified stroke patients admitted to 9 VA hospitals between April 1995 and March 1997. The Charlson Index was scored on the basis of discharge International Classification of Diseases, 9th Revision, Clinical Modification coding and dichotomized (low comorbidity 0 or 1 versus high ≥2) for analysis. Validity was assessed on the basis of modified Rankin score at hospital discharge (good outcome 0 or 1 versus poor ≥2 or dead) and 1-year mortality, adjusting for initial stroke severity. Results - Of the 960 enrolled ischemic stroke patients, 23% had a Charlson Index of 0, 34% 1, 22% 2, 12% 3, and 8% ≥4. Forty-eight percent of those with a low Charlson Index had a good outcome at discharge versus 37% of those with a high Charlson Index (P<0.001). For 1-year mortality, the proportions were 16% versus 26%, respectively (P<0.001). Logistic regression adjusting for initial stroke severity showed that those with a high Charlson Index had 36% increased odds of having a poor outcome at discharge (P=0.038) and 72% greater odds of death at 1 year (P=0.001). Every 1-point increase in Charlson Index was independently associated with a 15% increase in the odds of a poor outcome at discharge (P<0.005) and a 29% increase in the odds of death by 1 year (P<0.001). Conclusions - These data support the validity of the Charlson Index as a measure of comorbidity for use in ischemic stroke outcome studies.