Utility of Serum HBV RNA Measurement During Nucleoside/Nucleotide Analog Therapy in Chronic Hepatitis B Patients

Hepatitis B virus (HBV) particles containing HBV RNA are secreted into the blood; these RNA-containing particles are non-infectious byproducts of the replication cycle and are distinct from mature, DNA-containing virions. The proportion of these particles increases during nucleoside/nucleotide analog therapy, but the clinical significance of serum HBV RNA remains unclear. We evaluated longitudinal changes in serum HBV RNA and their association with the antiviral efficacy of nucleoside/nucleotide analog therapy. Eighty-six patients with chronic HBV infection (baseline HBV DNA ≥ 5.0 Log IU/mL and ALT < 500 U/L) treated with entecavir (ETV, N = 80) or tenofovir alafenamide (TAF, N = 6) were included. Serum HBV RNA was quantified using Cobas HBV RNA (RUO) at baseline, week 12, and week 48. Associations with clinical variables and treatment response were analyzed. Baseline HBV RNA correlated with HBsAg, HBV DNA, and hepatitis B core-related antigen. Both HBV DNA and RNA tended to decrease with advanced liver fibrosis. HBV DNA and RNA declines did not differ between HBeAg-positive and -negative patients, but the HBV RNA/DNA ratio at week 48 was significantly higher in HBeAg-positive cases (<i>p</i> < 0.001). Patients with baseline ALT ≥ 100 U/L showed significantly lower RNA levels at weeks 12 and 48 (<i>p</i> = 0.004, <i>p</i> < 0.001). While HBV DNA decline was similar between ETV and TAF (<i>p</i> = 0.076), RNA decline was significantly greater with TAF at week 12 (<i>p</i> = 0.027). Serum HBV RNA reflects intrahepatic viral replication and may not be influenced by fibrosis progression. HBV RNA decline during nucleoside/nucleotide analog therapy differed between ETV and TAF, suggesting drug-specific effects on viral RNA dynamics.