# A head-to-head comparison of the validity and predictive ability for health outcomes of diagnosis versus medication-based comorbidity indices

## TL;DR

This study compares two comorbidity indices, CCI and Rx-Risk, to determine which better predicts health outcomes like quality of life and hospitalization.

## Contribution

The study provides a direct comparison of CCI and Rx-Risk across multiple health outcomes using a single dataset.

## Key findings

- Rx-Risk showed stronger correlations with health-related quality of life and hospitalization risk than CCI.
- Rx-Risk outperformed CCI in predicting changes in quality of life and functional decline.
- Agreement between the two indices was poor for most conditions, except diabetes and chronic airway diseases.

## Abstract

Various comorbidity indices have been validated for individual health outcomes. However, systematic concurrent comparisons of multiple outcome measures in a single study remain relatively underrepresented but needed for practical decision support.

To compare the performance of the Charlson Comorbidity Index (CCI) and Rx-Risk Comorbidity Index (Rx-Risk).

Baseline and six-month follow-up data from n = 221 patients recruited in n = 70 practices were used. CCI and Rx-Risk scores were calculated using documented diagnoses and prescribed medications. Outcomes assessed were health-related quality of life (HRQoL, EQ-5D-5 L), functional impairment (B-ADL), cognitive decline (MMSE), and healthcare utilization (physician visits, hospitalizations). Indices performance was evaluated regarding agreement (Cohens Kappa (k)), known-groups validity (ANOVA, t-test), convergent validity (correlation coefficient (rs)) and predictive ability (R², Akaike information criterion (AIC)).

Patients were, on average, 80 years old, mostly female (55%), with 12 diagnoses and seven medications. Agreement between both indices was poor for all conditions except diabetes (k = 0.645) and chronic airway diseases (k = 0.486). Rx-Risk differed more in known groups, especially for HRQoL and hospitalizations, and showed stronger correlations with the EQ-5D index (rs, -0.215 vs. -0.134) and risk of hospitalization (rs, 0.145 vs. 0.128) than CCI. Rx-Risk, again, performed better in predicting the change of EQ-5D index (R², 30 vs. 28%) and all EQ-5D dimensions, functional (R², 55 vs. 52%) and cognitive decline (R², 47 vs. 46%) and physician consultations (AIC, 649.2 vs. 651.0), except for hospitalization (AIC, 149.2 vs. 147.1).

Rx-Risk demonstrated slightly superior validity and predictive ability for HRQoL and healthcare utilization, making it a promising option for studies focused on these outcomes. However, limitations regarding functional and cognitive impairment suggest alternative instruments are needed.

The online version contains supplementary material available at 10.1007/s40520-025-03073-w.