Hepatitis B virus

There are several tests used to detect the presence of hepatitis B antibodies. Antibodies are produced by the body in response to antigens(foreign proteins).

The hepatitis B surface antibody (anti-HBs) 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 found after successful vaccination. This test is done 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 an indicator of acute hepatitis B and frequently identifies infected people before symptoms appear. In some people (particularly those infected as children or those with a weak immune system, such as those with AIDS), chronic infection with HBV occurs.

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-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.

HBV DNA is a more sensitive test for detecting viruses in the blood stream. It is usually used in conjunction with – rather than instead of – the regular serological 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, IgM anti-HBc and HBsAg are usually requested 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 its own.

In those who are being treated for chronic HBV, HBeAg and HBV DNA can be used to determine whether the treatment is successful. 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.

All donated blood is tested for the presence of the HBsAg and HBV DNA 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 recovered from acute hepatitis and has rid themselves of the virus. 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 is less likely to 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. 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 IgM anti-HBc would be positive) or for some time (where IgM anti-HBc 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 1,000 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 or other scans (eg ultrasound scan) may be performed.