The causes of double-positive hepatitis B surface antigen antibody include: detection error, recovery period, virus mutation and so on. 1. Detection error: different manufacturers’ testing reagents and different testing methods may affect the test results, resulting in double-positive hepatitis B surface antigen antibody. 2. Recovery period: When the human body is infected by hepatitis B virus, it will activate the body’s immune system to produce protective antibodies against hepatitis B surface antigen (hepatitis B surface antibody). However, the appearance of hepatitis B surface antibody does not immediately clear all surface antigens, so in the recovery period, double-positive situation can occur. 3. Viral mutation: HBV itself is a highly mutable virus. Under the pressure of the body’s immunity and the pressure of antiviral drugs, it is more likely to mutate. The body produces antibodies after being infected with the hepatitis B virus, and then the virus mutates, resulting in double-positive hepatitis B surface antigen and antibody. Hepatitis B patients with double-positive symptoms, due to the complexity of the disease, but also increase the difficulty of treatment, it is recommended that you can be re-tested, and follow the doctor’s instructions to continue to take antiviral drugs for systematic treatment.