Evaluating the incident user design in the HIV population: Incident use versus naive?

The incident user design is the preferred study design in comparative effectiveness (CER) research. Usually, 180-365days of exposure free time is adequate to remove biases associated with inclusion of prevalent users. In HIV research, the use of antiretrovirals (ARVs) at any time in the past may influence future treatment choices and CER results; thus, identifying naive as opposed to incident users is of importance. We examined misclassification of antiretroviral naive status based on Medicaid administrative data through linkage to the UNC CFAR HIV Clinical Cohort (UCHCC). Methods: We identified Medicaid patients with incident exposure to common first-line ARV regimens between 2002 and 2008 that were also patients enrolled in the UCHCC. We calculated the proportion of antiretroviral naive patients based on the UCHCC, among patients identified as having incident exposure in Medicaid and examined factors associated with being antiretroviral naive in both data sources using logistic regression to generate prevalence odds ratios and associated 95% confidence intervals. Results: Of the 3500 Medicaid patients with incident antiretroviral (ARV) exposure, 1344 were also enrolled in the UCHCC. In this sample, 34% were antiretroviral naive at the time of first exposure in the Medicaid data based on the UCHCC. In multivariable models, higher CD4 cell counts and log HIV RNA values were associated with being antiretroviral naive in both data sources. Conclusions: Administrative data are an important source of information related to HIV treatment. As the construction of a durable and long-lasting HIV treatment plan involves knowledge of current and past antiretroviral therapy, augmentation of this data with comprehensive clinical cohort information is necessary.