Validity of the Updated Rx-Risk Index as a Disease Identification and Risk-Adjustment Tool for Use in Observational...

Identifying patient health conditions in observational studies is essential for accurately measuring healthcare practices and planning effective health policy interventions. This analysis evaluates the validity of the Rx-Risk Index, a tool that uses medication dispensing data to identify patient comorbidities and measure overall health. We examined an updated version of the Rx-Risk Index, reflecting changes in treatment practices, to assess its validity as a tool for identifying specific health conditions and as a measure of overall health to aid in risk adjustment in observational studies.

We conducted a validation study using two Australian linked health datasets, the Person-Level Integrated Data Asset (PLIDA) and the National Health Data Hub (NHDH), from 2010 to 2018, focusing on individuals aged 65 years or older. The sensitivity, specificity, PPV/NPV, Cohen's kappa, and F1 scores were used to assess agreement between Rx-Risk Index conditions and two reference standards: patient self-reported conditions and hospital diagnosis. The Rx-Risk Index's predictive validity for one-year mortality was also evaluated using logistic regression, with model fit assessed by AIC and c-statistic.

Data were analysed from 3,959 individuals in PLIDA and 157,709 individuals in NHDH. The Rx-Risk Index showed high sensitivity (≥75%) for diabetes, chronic airways disease, hyperlipidemia, and epilepsy against both self-reported conditions and hospital diagnoses. However, hyperlipidemia and hypertension showed lower specificity (<70%). High PPVs (≥78%) were observed for diabetes and renal failure. The agreement between the Rx-Risk Index and self-reported conditions was stronger (Cohen's kappa: 0.41-0.81 for 7 conditions) than between Rx-Risk Index and ICD10-AM diagnoses (kappa: 0.73 for one condition). The Rx-Risk Index was a strong predictor of one-year mortality, with c-statistic of 0.820 (95% CI: 0.817-0.825).

Selected Rx-Risk Index conditions are reasonable proxies for identifying specific conditions, particularly those requiring pharmacological management. The Rx-Risk Index was a strong predictor of one-year mortality, suggesting it is a valid measure of overall health. This study demonstrates the Rx-Risk Index's potential to enhance disease classification and risk adjustment in observational studies, supporting informed decision-making in health policy planning.