The HIV RNA test can detect HIV sooner than any other HIV test; as early as 9-11 days after exposure. The HIV 4th Generation test can detect HIV antibodies and antigens 3 weeks after exposure. The HIV RNA test detects the HIV virus in the blood by seeking out its genetic material (RNA), whereas the HIV 4th Generation Antibody test detects HIV antibodies and antigens. Antibodies are proteins created by the body’s immune system to try to destroy foreign substances like bacteria or viruses, in this case HIV. Antigens are the foreign substances that cause an immune response– the HIV Antibody test detects HIV p24 antigens.