Hepatitis B

How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?

How is it used?
There are many tests to detect antibodies against hepatitis B. Antibodies are produced by the body to protect it against antigens (foreign proteins). There are also many tests to detect viral antigens.

The most common test is for antibodies against the surface of the hepatitis B virus (anti-HBs). Their presence shows that the virus is absent and the person is not infectious. The antibodies also protect against future HBV infection. As well as exposure to HBV, the antibodies can also be the response to effective vaccination. This test is done to determine whether vaccination is needed (if anti-HBs is negative), to monitor the response to vaccination against the disease, or to follow an active infection.

Hepatitis B surface antigen (HBsAg) is an antigenic protein produced by HBV. This antigen is the earliest indicator of acute hepatitis B and can identify an infected person before symptoms appear. HBsAg disappears from the blood during recovery. In some people (particularly those infected as children or with a weakened immune system, such as people with AIDS), chronic HBV infection can develop, with HBsAg remaining positive.

Sometimes HBV “hides” in the liver and other cells and does not multiply, or does so at such a low level that it cannot be detected in the blood. These people are called healthy carriers. In other cases the body continues to produce viruses that can further infect the liver and other people. In both cases HBsAg will be positive. The next test can distinguish between these two states.

Hepatitis B e-antigen (HBeAg) is a viral protein associated with HBV infection. Unlike the surface antigen, the e-antigen is found in the blood only when the virus is also present. When the virus “hides”, the e-antigen disappears from the bloodstream. HBeAg is often used as a marker of the ability to spread the infection to other people (infectivity). Measuring HBeAg can also be useful for monitoring the effectiveness of HBV treatment; effective treatment will usually eliminate HBeAg from the blood and lead to the development of antibodies against the e-antigen (anti-HBe). There are some types (strains) of HBV that do not produce e-antigen; these are particularly common in the Middle East and Asia. In areas where these strains of HBV are common, measuring HBeAg is not very useful.

Anti-HBe is an antibody produced in response to the e-antigen. In people who have recovered from hepatitis B infection, anti-HBe will be present together with anti-HBc and anti-HBs. In people with chronic hepatitis B, anti-HBe usually becomes positive when the virus hides or is eliminated from the body. In people infected with strains that do not produce HBeAg, however, anti-HBe may be present.

Hepatitis B core antibody (anti-HBc) is an antibody against the core antigen of the hepatitis B virus. The core antigen is found on virus particles but disappears early in the infection. This antibody is produced during and after acute HBV infection and is usually found in chronic HBV carriers as well as in those who have cleared the virus, and it usually persists for life. The anti-HBc test is specific both for IgM immunoglobulins, anti-HBc IgM, which indicate acute infection, and for total antibodies, anti-HBc, which indicate a past infection, either acute or chronic.

The HBV DNA test is more sensitive than HBeAg for detecting the virus in the bloodstream. It is usually used alongside, not instead of, the standard blood tests. It can be used to monitor treatment of chronic HBV infection.

When is it requested?
These tests are used both to determine whether the vaccine has produced the desired level of immunity and to diagnose and follow the course of an infection.

In a patient with acute hepatitis, anti-HBc IgM and HBsAg are usually requested together to detect a recent HBV infection. In people with chronic hepatitis, or with high AST or ALT levels, HBsAg and anti-HBc are generally tested to check whether the liver damage is due to HBV. In this case HBsAg and HBeAg are measured at regular intervals (every six months or a year), since in some people HBeAg (and, less often, HBsAg) disappears spontaneously. Recent studies suggest that many people who are anti-HBc positive but HBsAg negative may have low levels of HBV DNA in their blood or liver. The reason for this is not yet known. In people being treated for HBV, HBeAg and HBV DNA can be used to see whether treatment has been successful (in which case they should disappear from the bloodstream). In people vaccinated against HBV, anti-HBs is used to check that vaccination has been successful; if antibody levels exceed 10 IU/ml, the person is protected for life against HBV infection, unless problems with their immune system develop (HIV infection, kidney failure or treatment with immunosuppressant medicines).

All units of blood are tested for HBsAg before use.

What does the test result mean?

• Surface antigen antibodies (anti-HBs): a positive result indicates immunity to the hepatitis B virus after 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 (or, at most, has an occult infection). A positive (or reactive) result indicates an active infection but does not predict whether other people can be infected.
• Hepatitis B e-antigen (HBeAg): a positive (or reactive) result indicates the presence of a virus that can be passed on to other people. A negative result usually means that the virus cannot be passed on to other people, except in countries where strains that generally do not produce this protein circulate.
• Hepatitis B core antibody (anti-HBc): if present together with positive anti-HBs, this usually indicates recovery from an infection, and the person is not a healthy carrier or chronically infected. In acute infection, the first type of antibody to HBc to appear is IgM. Testing for this type of antibody can show whether a person was infected with HBV recently (in which case the anti-HBc IgM test would be positive) or some time ago (in which case the anti-HBc IgM test would be negative).
• HBV DNA: a positive (or reactive) result indicates the presence of a virus that can be passed on to others. A negative result means that the virus cannot be spread to others, especially if tests are used that can detect as few as 200 virus copies per 1 mL of blood.

Is there anything else I should know?
While the tests described above are specific for HBV, other liver “function” tests such as AST, ALT and gamma-glutamyl transferase (GGT) can be used to monitor the progression of the disease. In some cases a liver biopsy may be done for confirmation.

1. If I might have HBV infection, do I need all these tests?
2. Should I be vaccinated?

1. If I might have HBV infection, do I need all these tests?
No. Your doctor will tell you which test or tests are most appropriate for your symptoms and medical history.

2. Should I be vaccinated?
Yes. Unless your medical history rules it out, it is wise to be vaccinated. Children routinely receive a series of doses, and it is considered appropriate to test them to check that they have become immune. The Centers for Disease Control and Prevention (CDC) does not recommend periodic measurement of anti-HBs antibodies in people who have developed immunity to HBV; even if their antibody titre falls below 10 IU/mL, they remain protected if exposed to the virus (unless problems with their immune system develop). The CDC does not recommend booster doses to keep antibody levels high.