The Impact of Medication-Based Risk Adjustment on the Association Between Veteran Health Outcomes and Dual Health System Use

Abstract

Background: Veterans commonly receive care from both Veterans Health Administration (VA) and non-VA sources (i.e., dual use). A major challenge in comparing health outcomes between dual users and VA-predominant users is applying an accurate method of risk adjustment.

Objective: To determine how different comorbidity indices affect the association between patterns of dual use and health outcomes.

Design: Retrospective cohort.

Participants: A total of 316,775 community-dwelling Veterans (≥65 years) with type 2 diabetes who were enrolled in VA and fee-for-service Medicare from 2008 to 2010.

Methods: We determined the associations between dual use and death or diabetes-related hospitalization in FY 2010 using multivariable models incorporating claims-based (Elixhauser) or medication-based (RxRisk-V) risk adjustment. Dual use was classified using four previously identified groups of health services users: 1) VA-predominant, 2) VA + Medicare visits and labs, 3) VA + Medicare test strips, and 4) VA + Medicare medications.

Key results: Controlling for Elixhauser comorbidities, dual-use groups 2-4 had significantly decreased odds of death or hospitalization compared to VA-predominant users. Controlling for RxRisk-V comorbidities, groups 2-4 had increased odds of death compared to VA-predominant users, but variable odds of hospitalization, with group 2 having increased odds (OR 1.06, CI 1.04-1.09), while groups 3 (OR 0.96, CI 0.94-0.99) and 4 (OR 0.93, CI 0.89-0.97) had decreased odds.

Conclusions: The method of risk adjustment drastically influences the direction of effect in health outcomes among dual users of VA and Medicare. These findings underscore the need for standardized and reliable risk adjustment methods that are not susceptible to measurement differences across different health systems.

Keywords: Medicare; Veterans; diabetes; health services research; outcomes.