There are several tests used to detect the presence of hepatitis B antibodies. Antibodies are produced by the body to offer protection from antigens (foreign proteins). There are also several tests that detect the presence of viral antigens.

The hepatitis B surface antibody (anti-HBs) is the most common test. Its presence indicates previous exposure to HBV, but the virus is no longer present and the person cannot pass on the virus to others. The antibody also protects the body from future HBV infection. In addition to exposure to HBV, the antibodies can also be acquired from successful vaccination. This test is done to determine the need for vaccination (if anti-HBs is absent), or following the completion of vaccination against the disease, or following an active infection.

Hepatitis B surface antigen (HBsAg) is a protein antigen produced by HBV. This antigen is the earliest indicator of acute hepatitis B and frequently identifies infected people before symptoms appear. HBsAg disappears from the blood during the recovery period. In some people (particularly those infected as children or those with a weak immune system, such as those with AIDS), chronic infection with HBV may occur and HBsAg remains positive.

Sometimes, HBV goes into “hiding” in the liver and other cells and does not produce new viruses that can infect others, or produces them in such low amounts that they cannot be found in the blood. People who have this form are said to be carriers. In other cases, the body continues to make viruses that can further infect the liver and can be spread to other people. In both these cases, HBsAg will be positive. The next test is helpful for distinguishing these two states.

Hepatitis B e-antigen (HBeAg) is a viral protein associated with HBV infections. Unlike the surface antigen, the e-antigen is found in the blood only when there are viruses also present. When the virus goes into “hiding,” the e-antigen will no longer be present in the blood. HBeAg is often used as a marker of ability to spread the virus to other people (infectivity). Measurement of e-antigen may also be used to monitor the effectiveness of HBV treatment; successful treatment will usually eliminate HBeAg from the blood and lead to development of antibodies against e-antigen (anti-HBe). There are some types (strains) of HBV that do not make e-antigen; these are especially common in the Middle East and Asia. In areas where these strains of HBV are common, testing for HBeAg is not very useful.

Anti-HBe is an antibody produced in response to the Hepatitis B e antigen. In those who have recovered from acute hepatitis B infection, anti-HBe will be present along with anti-HBc and anti-HBs. In those with chronic hepatitis B, usually anti-HBe becomes positive when the virus goes into hiding or is eliminated from the body. In strains that do not make HBe antigen, anti-HBe is also positive.

Anti-hepatitis B core antigen (anti-HBc) is an antibody to the hepatitis B core antigen. The core antigen is found on virus particles but disappears early in the course of infection. This antibody is produced during and after an acute HBV infection and is usually found in chronic HBV carriers as well as those who have cleared the virus, and usually persists for life. Anti-HBc testing is either specific for the IgM antibody, anti-HBc, IgM, which indicates acute infection, or measures total antibody, anti-HBC, which indicates past infection, either acute or chronic.

HBV DNA is a more sensitive test than HBeAg for detecting viruses in the blood stream. It is usually used in conjunction with – rather than instead of – the regular serologic tests. It may be used to monitor antiviral therapy in patients with chronic HBV infections.

These tests are used to determine whether the vaccine has produced the desired level of immunity as well as to diagnose and follow the course of an infection.

In a patient with acute hepatitis, anti-HBc IgM and HBsAg are usually ordered together to detect recent infection by HBV. In persons with chronic hepatitis, or with elevated ALT or AST, HBsAg and anti-HBc are usually done to see if the liver damage is due to HBV. If so, HBsAg and HBeAg are usually measured on a regular basis (every 6 months to a year), since in some people HBeAg (and, less commonly, HBsAg) will go away on their own. Recent evidence suggests that many of those who have anti-HBc but no HBsAg may have very low levels of HBV DNA in their blood and/or in their liver. The significance of this is still being debated. In those who are being treated for chronic HBV, HBeAg and HBV DNA can be used to determine whether the treatment is successful (in which case, both will become undetectable). If a person is given the HBV vaccine, anti-HBs is used to see if it successful; if levels of the antibody are over 10 IU/mL, the person is probably protected for life from infection by HBV, unless they have or develop problems with their immune system (such as HIV infection, renal failure, or treatment with drugs that suppress the immune system).

All donated blood is tested for the presence of the HBsAg before being distributed.

• Hepatitis B surface antibody (anti-HBs): a positive result indicates immunity to hepatitis B from the vaccination or recovery from an infection.
• Hepatitis B surface antigen (HBsAg): A negative result indicates that a person has never been exposed to the virus or has recovered from acute hepatitis and has rid themselves of the virus (or has, at most, an occult infection). A positive (or reactive) result indicates an active infection but does not indicate whether the virus can be passed to others.
• Hepatitis B e-antigen (HBeAg): A positive (or reactive) result indicates the presence of virus that can be passed to others. A negative result usually means the virus cannot be spread to others, except in parts of the world where infection with strains that cannot make this protein are common.
• Anti-hepatitis B core antigen (anti-HBc): If it is present with a positive anti-HBs, it usually indicates recovery from an infection and the person is not a carrier or chronically infected. In acute infection, the first type of antibody to HBc to appear is an IgM antibody. Testing for this type of antibody can prove whether a person has recently been infected by HBV (where anti-HBc, IgM would be positive) or for some time (where anti-HBc, IgM would be negative).
• HBV DNA: A positive (or reactive) result indicates the presence of virus that can be passed to others. A negative result usually means the virus cannot be spread to others, especially if tests that can pick up as few as 200 viruses (copies) in one mL of blood are used.

While the tests described above are specific for HBV, other liver function tests such as AST, ALT, and gamma-glutamyl transferase (GGT) may be used to monitor the progress of the disease. In some cases, a liver biopsy may be performed for confirmation.