The clinical utility of two biomarkers, hepatitis B virus (HBV) RNA and hepatitis B core‐related antigen (HBcrAg), as compared to conventional markers of HBV replication and disease activity, is unclear.

Untreated participants in the North American Hepatitis B Research Network Adult Cohort Study were categorized by chronic hepatitis B (CHB) phases based on HBsAg and HBeAg status and HBV DNA and alanine aminotransferase (ALT) levels. HBV RNA and HBcrAg were measured (Abbott HBV pgRNA Research Assay and Fujirebio Lumipulse Immunoassay, respectively), and cross‐sectional associations with conventional CHB markers were tested. Among 1,409 participants across all CHB phases, median HBV DNA was 3.8 log₁₀ IU/mL and ALT was 34 U/L. HBV RNA was quantifiable in 99% of HBeAg⁺ and 58% of HBeAg⁻ participants; HBcrAg was quantifiable in 20% of HBeAg⁺ (above linear range in the other 80%) and 51% of HBeAg⁻ participants. Both markers differed across CHB phases (P < 0.001), with higher levels in the HBeAg⁺ and HBeAg⁻ immune active phases. HBV RNA and HBcrAg correlated moderately strongly with HBV DNA in both HBeAg⁺ and HBeAg⁻ phases (HBV RNA: e⁺ ρ = 0.84; e⁻ ρ = 0.78; HBcrAg: e⁺ ρ = 0.66; e⁻ ρ = 0.56; P for all, <0.001), but with HBsAg levels among HBeAg⁺ phases only (HBV RNA: e⁺ ρ = 0.71; P < 0.001; e⁻ ρ = 0.18; P = 0.56; HBcrAg: e⁺ ρ = 0.51; P < 0.001; e⁻ ρ = 0.27; P < 0.001). Associations of higher HBV RNA and HBcrAg levels with higher ALT, APRI, and Fibrosis‐4 levels were consistent in HBeAg⁻, but not HBeAg⁺, phases.

Despite clear relationships between HBV RNA and HBcrAg levels and CHB phases, these markers have limited additional value in differentiating CHB phases because of their strong association with HBV DNA and, to a lesser extent, with clinical disease indicators.