How is it used?
Hepatitis B tests may be used for a variety of reasons. Some of the tests detect antibodies produced in response to HBV infection; some detect antigens produced by the virus, and others detect viral DNA.
Generally, one set of tests is used to determine the cause of acute symptoms while another set of tests may be used after a diagnosis is made, to monitor possible progression of the disease, to detect chronic infection and/or carrier status.
The items below list the main uses for HBV tests:
- To detect acute hepatitis B infection: hepatitis B surface antigen (HBsAg), hepatitis B core antibody (anti-HBc), IgM and sometimes hepatitis B e antigen (HBeAg)
- To diagnose chronic HBV hepatitis: HBsAg, hepatitis B virus (HBV) DNA, and sometimes HBeAg
- To monitor chronic hepatitis B infection and its treatment: HBsAg, hepatitis B e antigen (HBeAg), hepatitis B surface antibody (anti-HBs) IgG, hepatitis B e antibody (anti-HBe) IgG and HBV DNA
- To detect previous exposure to hepatitis B, in a person who is immune compromised (when the virus can become reactivated): hepatitis B core antibody (anti-HBc) total and anti-HBs
Some of the secondary reasons to perform testing include: to screen for hepatitis B infection in at-risk populations or in blood donors, to determine if someone is a carrier, to detect previous infection (with subsequent immunity), and to determine if immunity has developed due to vaccination.
Some of the tests used to screen for infection may be performed as part of an acute viral hepatitis panel in conjunction with tests for other hepatitis viruses, including hepatitis A (HAV) or hepatitis C (HCV).
When is it ordered?
Hepatitis B tests may be ordered when someone has signs and symptoms associated with acute hepatitis to determine if they are due to infection with HBV. Some of these include:
- Loss of appetite
- Nausea, vomiting
- Abdominal pain
- Dark urine
- Pale stools
- Joint pain
Hepatitis B tests may be done as follow up when routine tests results such as ALT and/or AST are elevated. Sometimes acute forms of hepatitis may be detected this way since they may cause only mild symptoms that can be confused with the flu. Chronic hepatitis more often has no symptoms and is more commonly detected when routine test results are abnormal.
A test for hepatitis B surface antigen (HBsAg) may be used for screening when someone falls into one of the high-risk categories for chronic hepatitis B. In September 2008, the CDC revised it guidelines and recommends the following groups be tested for HBsAg:
- People who are possible source of infection through accidental cuts, needlesticks, etc. in health care workers
- People born in areas of the world that have a greater than 2% prevalence of HbsAg (for example, much of Asia and Africa)
- People born in the US but were not vaccinated and whose parents are from an area with greater than 8% prevalence of HbsAg
- Men who have sex with men
- People who have elevated liver enzymes (ALT and AST) with no known cause
- People with certain medical conditions that require that their immune system be suppressed
- Pregnant women
- People who are in close contact with someone infected with HBV
- Those infected with HIV
In addition, some states in the US recommend that people who are in contact with the public and who are a possible source of infection through accidental cuts, scrapes, etc. be screened.
When hepatitis B tests are used to monitor people with chronic hepatitis B infections, they may be performed on a regular basis. Hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) are usually measured about every 6 months to a year, since in some people HBeAg (and, less commonly, HBsAg) will go away on their own. In those who are being treated for chronic HBV, HBeAg and HBV DNA can be used to determine whether the treatment is successful. HBV DNA will fall, usually to undetectable levels, with successful treatment. If HBeAg was positive before treatment and becomes negative, then treatment may sometimes be stopped after a further period of treatment, and both it and HBV DNA may remain undetectable. If HBeAg was negative before treatment or remains positive, then treatment is usually continued.
All donated blood is tested for the presence of the HBsAg before being distributed for transfusion.
Is there anything else I should know?
Even if you don’t have symptoms, an HBV infection can damage your liver and you can spread the infection to others. For this reason, it is important to get tested if you think you have been exposed to HBV.
Hepatitis D (HDV) is another virus that can cause liver infections, but only if hepatits B is also present. A person may become infected with both viruses at the same time (a co-infection) or may first be infected with hepatitis B and then become infected with HDV (a superinfection). In the U.S., the incidence of HDV is low. There is no vaccine for HDV, but since it causes infections only in the presence of HBV, it may be prevented with the HBV vaccine.