This test is usually the first one used to detect infection with HIV. If antibodies to HIV are present (positive), the test is usually repeated to confirm the diagnosis. If ELISA is negative, other tests usually aren't needed. This test has a low chance of having a false result after the first few weeks that a person is infected. This test looks for hepatitis B surface antigens in your blood. The test is used to find out whether you have a recent or long-standing infection from the hepatitis B virus (HBV). HBV has proteins called antigens on its surface that cause your immune system to make antibodies. Hepatitis B surface antigens can be found in your blood within several weeks after the infection starts. They are one of the earliest signs of a hepatitis B infection.