Management of hepatitis B virus (HBV) reactivation in patients with resolved HBV infection based on a highly sensitive HB core‐related antigen assay

Aims To prevent hepatitis B virus (HBV) reactivation‐related hepatitis, we examined the clinical usefulness of a highly sensitive HB core‐related antigen (iTACT‐HBcrAg) assay in patients with resolved HBV infection after nucleos(t)ide analog (NA) treatment for HBV reactivation. Methods We retrospectively analyzed 27 patients with resolved HBV infection who experienced HBV reactivation (defined as HBV DNA levels of 1.3 log IU/ml or more), and who received systemic chemotherapies for hematological malignancies between 2008 and 2020. iTACT‐HBcrAg, HBsAg‐HQ, and antibodies against hepatitis B surface antigen (anti‐HBs) were measured using samples stored after HBV reactivation. The lower limit of quantification for iTACT‐HBcrAg was 2.0 log U/ml. Results HBV reactivation was diagnosed at a median HBV DNA level of 1.8 log IU/ml, and then all patients received NA treatment. No patient had HBV‐related hepatitis with a median maximum HBV DNA level of 2.0 log IU/ml. The positivities of iTACT‐HBcrAg and HBsAg‐HQ were 96% and 52% after HBV reactivation, respectively. Of 25 patients with detectable iTACT‐HBcrAg at the initiation of NA treatment, 17 (68%) achieved iTACT‐HBcrAg loss. Median durations from NA treatment to HBV DNA loss and iTACT‐HBcrAg loss or the last follow‐up were 35 and 175 days, respectively. Recurrence of HBV reactivation after NA cessation was not observed in seven of eight patients who achieved iTACT‐HBcrAg loss or seropositive for anti‐HBs during follow‐up, except for one without anti‐HBs after allogeneic transplantation. Conclusions iTACT‐HBcrAg could be a potential surrogate marker for diagnosing early‐stage HBV reactivation as well as safe cessation of NA treatment in patients with resolved HBV infection after HBV reactivation.