Comparing major comorbidity indices as predictors of all-cause mortality in the Veterans Affairs health care system

Objectives

The Charlson Comorbidity Index (CCI), the Elixhauser Comorbidity Index (ECI), and the Functional Comorbidity Index (FCI) are validated clinical measures of comorbidity, but direct comparisons between these measures have rarely been studied especially in high-risk patient populations, such as homeless individuals. The US Department of Veterans Affairs (VA) offers large patient samples to compare these comorbidity measures as predictors of mortality using administrative and clinical records. We examined CCI, ECI, and FCI scores among veterans seeking VA healthcare services, including those experiencing homelessness, and compared their predictive value in relation to all-cause mortality risk.

Study Design and Setting

Several VA databases from 2017 to 2021 were retrospectively linked, and 4,701,711 U S. veterans [308,553 with homelessness and 4,393,158 without homelessness] were evaluated over a median follow-up of 4.1 years, yielding 917,921 recorded deaths. Regression models were constructed, and Harrell's Concordance Statistic (HCS) was calculated that assessed the ability of z-transformed comorbidity scores to discriminate “high-risk” vs “low-risk” groups of patients for mortality risk, after adjustment for demographic and clinical characteristics.

Results

In adjusted models, ECI (HCS: 0.76–0.77) and CCI (HCS: 0.75–0.76) were better able to discriminate “high-risk” vs “low-risk” groups than FCI (HCS: 0.72–0.75) among homeless and nonhomeless veterans. Compared to ECI and CCI, FCI was more strongly associated with homelessness.

Conclusion

CCI and ECI may be more predictive of all-cause mortality risk than FCI, although FCI may be a useful measure of functioning in homeless populations.

Plain Language Summary

The CCI, ECI, and FCI are clinical measures of comorbidity, but their direct comparisons have been limited, especially in high-risk patient populations like homeless individuals. This study examined CCI, ECI, and FCI scores among veterans seeking health care services at the US Department of Veterans Affairs and found that ECI and CCI were better at discriminating high-risk vs low-risk groups and predicting mortality among homeless and nonhomeless veterans.