Hepatitis B virus DNA is an indicator of infectiousness by monitoring the level of hepatitis B virus DNA in the blood. HBVDNA is the core substance of hepatitis B virus and the basis of viral replication, and is the most direct, specific and sensitive indicator of HBV infection. positive HBVDNA indicates the presence of HBV replication in the body, and higher levels indicate stronger viral replication and greater infectivity. In addition, HBVDNA test can provide a reliable basis for clinical antiviral treatment decision making and assessment of efficacy, for example, for HBeAg-positive patients with chronic hepatitis B, when their serum HBVDNA>1x10E5copies/ml and transaminases are elevated more than twice the normal value, antiviral treatment should be started; HBVDNA negative is a sign to judge the effectiveness of antiviral treatment. If HBVDNA changes from negative to positive during the course of treatment, it indicates the occurrence of viral resistance and the need to add or switch to other antiviral drugs. The HBVDNA test is reported in two main ways: qualitative, which determines whether it is negative or positive, and its normal value is negative; and quantitative, which detects the amount of hepatitis B virus in the blood. The unit is usually expressed as “copies/ml”, “copies/ml” or “IU/ml” on the report form, generally expressed as χ x 10E IU/ml (or copies/ml), where χ indicates the base number and E indicates a multiple of 10, e.g. the result is 3.75x10E4copies/ml, which means 3.75 multiplied by 4 times 10, i.e. 37500 hepatitis B viruses. The normal value of domestic kits is generally <1x10*3copies/ml; the lower line of detection of imported kits is <20IU/ml, and the method is more sensitive and accurate. Due to the strict and sensitive requirements of DNA testing technology, it is easy to be interfered with, and there is a possibility of false positive test results. And different blood specimens from the same person may have different test results, so if necessary, you can retest or change hospitals to check again. Therefore, once the HBVDNA is confirmed to be positive, it indicates the presence of hepatitis B virus replication in the body, which is contagious, and further diagnosis and treatment should be carried out promptly at an infectious disease specialist.