LAUSR

The risk of hepatitis B virus (HBV) reactivation has increased owing to advances in the immunosuppressive therapy field. However, the HBV reactivation incidence among patients with previously resolved HBV (prHBV) infection during immunosuppressive therapy for rheumatoid arthritis (RA) remains unclear. The objective of this work is to describe the validity of detecting prHBV infection from administrative data through comparisons with chart abstraction and determine the incidence of HBV reactivation during immunosuppressive therapy for RA in Japan. In this retrospective cohort study, data on selected patients were extracted from administrative claims data. To identify patients with prHBV infection and de novo hepatitis, and HBsAg carriers, we conducted chart abstraction. The incidence rate of de novo hepatitis was 1.23 of 100 person‐years. The positive predictive value (PPV) and its 95% confidence interval (CI) of administrative data for the identification of suspected prHBV infections was 85.8% (95% CI: 81.7%‐89.3%). This study evaluated the PPV of the algorithm of HBV‐DNA testing with immunosuppressive therapy performed four times or more per year for the detection of prHBV infection from administrative data. Additionally, we determined the incidence rate of HBV reactivation among preHBV infections during immunosuppressive therapy for RA to be 1.23 of 100 person‐years.