Used in diagnostic assays to detect Hepatitis B surface antigen (HBsAg) in human serum or plasma. Plays a critical role in confirming the presence of active Hepatitis B virus infection. Commonly employed in immunoassay development, including ELISA and lateral flow tests, for high sensitivity and specificity. Also utilized in quality control of HBsAg test kits and for calibration of automated diagnostic platforms. Supports research in virology and vaccine efficacy studies by enabling accurate measurement of antigen-antibody interactions.