The research plan aims to evaluate the consistency of the digital PCR-based hepatitis B virus nucleic acid quantification technique with the existing Roche qPCR-based detection method. Approximately 200 samples of residual serum from patients with chronic hepatitis B, covering high, medium, low, and those below the Roche lower limit concentration or undetectable, will be collected. The two methods will be used for parallel testing. The main objective is to evaluate the quantitative consistency of the two methods within the quantifiable range of Roche (≥ 20 IU/mL); the secondary objectives include evaluating the qualitative detection rate of samples with concentrations below 20 IU/mL or undetectable nucleic acid.

The study aims to include a total sample size of approximately 200 cases: 100 positive cases: ≥ 1000 IU/mL: 40 cases; 100 - 1000 IU/mL: 30 cases; 20 - 100 IU/mL: 30 cases; 100 negative cases: lower than 20 IU/mL: 40 cases, and undetected: 60 cases. Collect the age, gender, duration of HBV infection, antiviral treatment drugs and treatment courses, HBeAg status, HBsAg quantification (if available), ALT/AST levels, date of blood sample collection, date and result of combas HBV DNA detection, and digital PCR detection results of the enrolled patients. By comparing the detection results of the two methods, evaluate the quantitative accuracy or qualitative detection ability of the digital PCR hepatitis B detection method.

Inclusion Criteria:

1. Patients who have been diagnosed with chronic hepatitis B (in accordance with the diagnostic criteria of the "Chronic Hepatitis B Prevention and Treatment Guidelines (2022 Edition)") and are currently receiving NAs antiviral treatment for ≥ 6 months or have not received treatment and are ≥ 18 years old;
2. Remaining samples (serum) that have undergone combas HBV DNA testing and have clear test results, with the sample collection time frozen for ≤ 6 months;
3. The remaining sample volume is sufficient (≥ 1.0 mL), sufficient for digital PCR testing and necessary duplicate testing;
4. Samples from the same patient at different time points can be included as independent samples, but the sampling interval time needs to be recorded.

Exclusion Criteria:

1. Combine other liver virus infections such as HCV, HDV or HIV;
2. Poor sample quality, such as severe hemolysis, lipemia or repeated freezing and thawing ≥ 3 times;
3. The samples were not properly frozen and stored (-80℃) after collection or the temperature records were missing;
4. The clinical information is severely lacking, making it impossible to confirm the diagnosis and treatment status;
5. The duplicate samples already included at the same time point (only the first included sample is retained).

The research samples were derived from the routine diagnostic leftover serum samples of chronic hepatitis B patients who were treated at the outpatient or inpatient departments of Beijing Ditan Hospital, Capital Medical University. All the samples were the leftover samples obtained after the routine HBV DNA testing (combas HBV) was completed, and they were the secondary utilization of the leftover samples from clinical routine tests.