To diagnose and follow the course of an infection with hepatitis B or to determine if the vaccine against hepatitis B has produced the desired level of immunity. This test is useful for evaluation of possible immunity in individuals who are at increased risks for exposure to hepatitis B. Ways to contract Hepatitis B is by coming in contact with an infected person's blood, semen or other body fluid. If you contract this virus you may feel like you have the flu or you may not show any symptoms at all.