This test looks for antibodies called IgM in your blood. The test is used to find out whether you are actively infected with the hepatitis B virus (HBV).
HBV has a central core and a surrounding envelope. Your immune system makes IgM antibodies to the core of HBV during the active stage of infection. Hepatitis B core IgM antibodies begin to appear in your blood several weeks after you are first infected with HBV. People who have had the hepatitis B vaccine will not have the core antibody in their blood.
HBV is one of 5 hepatitis viruses. The others are hepatitis A, C, D, and E. Most hepatitis infections are caused by these 5 viruses. HBV is spread through blood, seminal fluid, and vaginal secretions. It can take 60 to 150 days to develop symptoms of hepatitis B after you become infected. The virus causes an infection in the liver. In most cases, this virus clears up on its own within 6 months. But in a small portion of adults and a larger portion of children, the virus does not go away. This is especially true for newborns. This is called having a chronic infection. It may lead to liver cell damage; scarring, or cirrhosis; or liver cancer.