Construction and characteristics of the RxRisk-V - A VA-adapted pharmacy-based case-mix instrument

BACKGROUND. Assessment of disease burden is the key to many aspects of health care management. Patient diagnoses are commonly used for case-mix assessment. However, issues pertaining to diagnostic data availability and reliability make pharmacy-based strategies attractive. Our goal was to provide a reliable and valid pharmacy-based case-mix classification system for chronic diseases found in the Veterans Health Administration (VHA) population. OBJECTIVE. To detail the development and category definitions of a VA-adapted version of the RxRisk (formerly the Chronic Disease Score); to describe category prevalence and reliability; to check category criterion validity against ICD-9 diagnoses; and to assess category-specific regression coefficients in concurrent and prospective cost models. RESEARCH DESIGN. Clinical and pharmacological review followed by cohort analysis of diagnostic, pharmacy, and utilization databases. SUBJECTS. 126,075 veteran users of VHA services in Washington, Oregon, Idaho, and Alaska. METHODS. We used Kappa statistics to evaluate RxRisk category reliability and criterion validity, and multivariate regression to estimate concurrent and prospective cost models. RESULTS. The RxRisk-V classified 70.5% of the VHA Northwest Network 1998 users into an average of 2.61 categories. Of the 45 classes, 33 classes had good-excellent 1-year reliability and 25 classes had good-excellent criterion validity against ICD-9 diagnoses. The RxRisk-V accounts for a distinct proportion of the variance in concurrent (R-2 = 0.18) and prospective cost (R-2 = 0.10) models. CONCLUSIONS. The RxRisk-V provides a reliable and valid method for administrators to describe and understand better chronic disease burden of their treated populations. Tailoring to the VHA permits assessment of disease burden specific to this population.