This kit is used for quantitative determination of HBsAg in human serum or plasma in vitro. Hepatitis B surface antigen (HBsAg) is the outer membrane protein of hepatitis B virus and the first HBV marker in serum. If it does not disappear after 6 months, it can become a carrier of chronic hepatitis (CH) or HBsAg and last for several years or decades. It can not be used as the only index for the evaluation of patients' condition. It needs to be combined with the clinical manifestations of patients and other laboratory tests for comprehensive analysis of the condition.