HIV antigen is also known as HIV P24 antigen. The use of anti-HIVP24 antigen monoclonal antibody preparation reagents to detect HIVP24 antigen in the serum by ELISA is helpful for diagnosis during the window of antibody production. Currently, we have a four-generation test, the combined HIV antigen-antibody test, which can confirm the diagnosis by detecting HIV antigen and antibody in the infected person’s body about 2-3 weeks after HIV infection, while it takes about 3-4 weeks to detect the antibody alone. Therefore, the combined antigen and antibody test can speed up the detection time and shorten the window period.