Estimating optimal thresholds for adherence to RASA medications among older adults with hypertension

The Centers for Medicare and Medicaid Services (CMS) Star Ratings program incentivizes health plans in Medicare to improve performance on a variety of quality measures such as adherence to renin-angiotensin system antagonists (RASAs). Adherence to RASA medications, defined as having a proportion of days covered (PDC) of at least 80%, has been improving for several years, suggesting that further investigation is needed to assess the appropriateness of the current 80% PDC threshold for medication adherence as an indicator of quality. The 80% PDC threshold has been found to be associated with improved health care resource utilization outcomes; however, little evidence exists to show that this threshold is optimal.

To evaluate the association between adherence to RASA medications and health care resource utilization outcomes within a Medicare Advantage population and to identify the optimal PDC threshold that maximizes economic and utilization benefits.

This retrospective cohort study used de-identified administrative claims data from the 2015 to 2018 in Optum's de-identified Clinformatics Data Mart Database. Inclusion in the study was based on measure specifications for the RASA adherence measure used in the Medicare Part D Star Ratings program. Adherence was assessed over a 1-year period, and health care utilization and medical costs were assessed in the subsequent year. Multivariable logistic regression models were used to assess the relationship between adherence and economic outcomes after accounting for hypothesized confounders.

A total of 1,006,901 individuals were included in the study with an average PDC of 87.5% (SD = 17.8%). During the follow-up period, 12.1% of individuals experienced a hospitalization, 14.81% used an emergency department (ED), and 32.3% visited a non-ED outpatient facility. Each percentage point increase in PDC was significantly associated with decreased odds of hospitalization (odds ratio [OR] = 0.997; 95% CI = 0.997-0.997) and ED visit (OR = 0.997; 95% CI = 0.996-0.997), being in the top decile of payer medical costs (OR = 0.998; 95% CI = 0.997-0.998), and increased odds of outpatient visits (adjusted OR = 1.001; 95% CI = 1.001-1.002). Receiver operator characteristic curve analyses found the optimal PDC thresholds to be 91.5%, 90.7%, 90.7%, and 90.4% for hospitalization (area under the curve [AUC] = 0.527), ED visit (AUC = 0.534), outpatient visit (AUC = 0.501), and medical costs (AUC = 0.532), respectively.

This study demonstrated the importance of medication adherence for preventing undesirable outcomes, such as future hospitalizations, ED visits, and high medical costs, among individuals with hypertension enrolled in Medicare Advantage. The optimal threshold for PDC related to health care resource utilization outcomes was found to be greater than that used in the measure in CMS Star Ratings. Future research should examine the impact of changes in adherence thresholds for economic and clinical outcomes.