Circulating HBV RNA Tracks the Active Hepatitis B Reservoir More Closely Than HBsAg
A measurable blood biomarker that mirrors hepatitis B virus cccDNA activity has long been missing from routine chronic hepatitis B care. This study positions circulating HBV RNA, or cirB-RNA, as a practical candidate for that role, especially in patients whose viral replication is partially suppressed by nucleos(t)ide analogues.
Investigators paired serum and liver biopsy samples from 152 adults with chronic hepatitis B, including 122 untreated patients and 30 receiving nucleos(t)ide analogue therapy. They quantified cirB-RNA with an investigational assay adapted for the cobas 6800 system, then compared those measurements with intrahepatic markers of viral transcription, serum HBV DNA, HBsAg, HBcrAg, and alanine aminotransferase.
The central clinical point is straightforward. CirB-RNA behaved like a marker of active viral transcription from the intrahepatic reservoir, not like a blunt measure of total antigen burden.
Detectability Dropped as Viral Activity Became More Restricted
cirB-RNA was detectable in all patients with HBeAg-positive chronic hepatitis, but detection rates fell sharply in the other groups. Among untreated HBeAg-negative chronic hepatitis patients, 57% had detectable cirB-RNA, while only 14% of untreated chronic infection patients did. In the nucleos(t)ide analogue–treated cohort, cirB-RNA remained detectable in 47%.
Those gradients fit the biology of chronic hepatitis B. HBeAg positivity usually reflects a more transcriptionally active viral state, with greater cccDNA output and more abundant viral RNA species entering the circulation. As the infection settles into lower-replication phases, or as polymerase inhibition suppresses new DNA synthesis, circulating RNA becomes harder to detect because the upstream transcriptional machinery is less active.
This is where the assay has potential bedside value. A blood marker that fades when cccDNA-driven transcription is quiet could help clinicians distinguish patients with a genuinely quiescent reservoir from those who still carry transcriptionally active virus despite low or suppressed HBV DNA.
HBV RNA Outperformed HBsAg for Reflecting Transcriptional Activity
Undetectable cirB-RNA aligned with lower intrahepatic cccDNA transcriptional activity and lower serum HBcrAg in both untreated and treated patients. In contrast, HBsAg did not separate these groups in the same way.
That separation matters because HBsAg is often treated as a proxy for viral burden, yet surface antigen can persist through pathways that do not map cleanly onto current transcriptional activity. HBV RNA offers a more direct readout of what the cccDNA minichromosome is actually producing. In practical terms, that makes cirB-RNA conceptually closer to an activity marker than a stockpile marker.
The liver data reinforce that interpretation. cccDNA and 3.5 kb RNA were measured directly in paired biopsy tissue, allowing the serum assay to be judged against the source of transcription rather than against serum markers alone. When cirB-RNA was absent, the tissue profile was consistent with a lower active reservoir.
Untreated HBeAg-Negative Patients Showed the Strongest Correlation Pattern
The most informative subgroup was the untreated HBeAg-negative cohort. In those patients, cirB-RNA correlated with intrahepatic 3.5 kb RNA and cccDNA transcriptional activity, as well as with serum HBV DNA and HBcrAg. It did not correlate with HBsAg or with total cccDNA levels.
That pattern points to a subtle but important distinction. Total cccDNA quantity is not the same as transcriptional output. A patient may harbor cccDNA in hepatocytes without generating much active RNA from that reservoir, and a marker tied to transcription should track the latter rather than raw copy number. The correlation with HBV DNA also makes biological sense, since DNA production remains downstream of active transcription and reverse transcription.
One sentence captures the practical consequence: cirB-RNA is reading out the activity of the reservoir, not just its presence.
Dual Negativity Identified the Lowest-Activity Reservoir
Among untreated HBeAg-negative patients, combined undetectability of cirB-RNA and HBcrAg identified a subgroup with the lowest levels of intrahepatic transcriptionally active cccDNA. This dual-marker approach may be more informative than either assay alone, because each reflects a different aspect of viral expression.
HBcrAg has already been used as a surrogate of intrahepatic viral activity, and pairing it with cirB-RNA appears to sharpen the biological signal. When both are absent, the data suggest a particularly quiet viral reservoir. For chronic hepatitis B management, that could matter when deciding how to interpret long-term suppression, estimate residual activity, or stratify patients for studies of cure-directed therapy.
The finding also has a pathophysiologic logic. cccDNA serves as the stable nuclear template for viral transcription, while circulating RNA fragments appear to represent material produced from that template. If both markers fall below detection, the reservoir is likely producing very little transcriptionally active virus.
A Biomarker Built for Treated and Untreated Disease
The treated cohort deserves attention because nucleos(t)ide analogues suppress HBV DNA without eliminating cccDNA. A biomarker that still performs in that setting could fill an important gap. Nearly half of the treated patients still had detectable cirB-RNA, meaning antiviral suppression did not erase the transcriptional signal in every case.
This is clinically relevant because standard therapy leaves behind a residual viral reservoir. Even when HBV DNA is suppressed, cccDNA can persist in hepatocytes and continue to generate viral products at low levels. A serum RNA assay that continues to register this activity may help separate pharmacologic suppression from true biologic quiescence.
The study does not claim that cirB-RNA is ready to replace existing tools, and it does not establish a treatment algorithm. What it does show is that a serum assay can reflect intrahepatic transcriptional activity with enough fidelity to make it a serious candidate biomarker for chronic hepatitis B research and, eventually, clinical monitoring.
What the Data Support Now
The data support a simple interpretation: circulating HBV RNA is a meaningful indicator of the active intrahepatic HBV reservoir in both untreated and nucleos(t)ide analogue–treated chronic hepatitis B. Its strongest value appears to be in HBeAg-negative disease, where conventional serum markers can be less informative about ongoing cccDNA transcription.
The remaining gaps are practical rather than conceptual. Larger validation cohorts, standardized assay performance, and longitudinal outcome data will be needed before cirB-RNA can be placed into routine management pathways. For now, the study provides a biologically coherent serum marker that aligns with intrahepatic viral activity more closely than HBsAg and, in key subgroups, more closely than total cccDNA quantity.