There are several tests used to detect the presence of hepatitis B . Antibodies are produced by the body in response to (foreign proteins).
The hepatitis B surface antibody (anti-HBs) indicates previous exposure to HBV, but the 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, these antibodies can also be found after successful . 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 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 may occur.
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 . 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 easily 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. This is a useful test to distinguish people who have anti-HBs due to past infection (in whom it will be positive) from those who have anti-HBs due to vaccination (in whom it will be negative).
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 has produced the desired level of 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 mIU/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.