A reactive hepatitis B surface antigen, or HBsAg, result means that the hepatitis B virus is present and the person is infected. According to the Hepatitis B Foundation, the infection can either be acute or chronic and those individuals infected with the virus can pass it to other people.
Hepatitis B is transmitted through the blood and bodily fluids of an infected person. There is a blood test to screen for hepatitis B, which is called the "hepatitis B blood panel," and is comprised of three different tests: HBsAg, which tests for a current infection; hepatitis B surface antibody, or HBsAb, which tests for a patient's response to the vaccine or indicates that the patient has recovered from the virus; and hepatitis B core antibody, or HBcAB, which shows the patient either had a past infection or is currently infected. Sometimes this result is a false positive, but is used in conjunction with the two other tests to indicate which stage the patient is at.