This test is used to help diagnose a liver infection due to the hepatitis A virus (HAV). There are several causes of hepatitis and the accompanying symptoms, so this test may be used to determine if the symptoms are due to hepatitis A.
A few different versions of the test may be used to detect different classes of hepatitis A antibodies.
The HAV IgM antibody test detects the first antibody produced by the body when it is exposed to hepatitis A. This test is used to detect early or recent infections and to diagnose the disease in people with symptoms of acute hepatitis. It may be performed as part of an acute viral hepatitis panel.
The HAV IgG test detects the IgG antibodies that develop later in the course of the disease. IgG antibodies remain present for many years, usually for life, providing protection against recurrent infection by the same virus. The IgG test is used to detect past HAV infections and may occasionally be used to determine if an individual has developed immunity from a previous infection (immune status), in which case a vaccine is not necessary.
The total HAV antibody test detects both IgM and IgG antibodies and thus may be used to identify both current and past infections. This test will also be positive after receiving the vaccine, so sometimes it may be used to determine whether a person has developed immunity after vaccination, though this practice is not advised. Recommendations of the Advisory Committee on Immunization Practices (ACIP) state that "post-vaccination testing is not indicated because of the high rate of vaccine response among adults and children. In addition, not all testing methods approved for routine diagnostic use in the United States have the sensitivity to detect low anti-HAV concentrations after vaccination."
In acute hepatitis, other tests such as bilirubin, liver panel, ALT, and AST may be performed with viral hepatitis tests to help diagnose the condition.
In some people and in many young children, hepatitis A may not cause any symptoms. Children infected by HAV often have very mild symptoms, such as fever and diarrhea, and are often thought to have "flu."
An HAV test may also be ordered when a person is likely to have been exposed to the virus regardless of whether symptoms are present or not.
No active infection but previous HAV exposure; has developed immunity to HAV or recently vaccinated for HAV
Has been exposed to HAV but does not rule out acute infection
No current or previous HAV infection; vaccine may be recommended if at risk
A total antibody test detects both IgM and IgG antibodies but does not distinguish between them.
If the total antibody test or hepatitis A IgG result is positive and someone has never been vaccinated against HAV, then the person has had past exposure to the virus. About 30% of adults over age 40 have antibodies to hepatitis A.
Although hepatitis A IgM antibodies are considered diagnostic for acute infection with hepatitis A, there has been increasing use of the test in people who do not have signs and symptoms of acute hepatitis. The Centers for Disease Control and Prevention have recommended that the test only be used for persons who clinically have acute hepatitis to decrease the possibility of falsely positive results.
This article was last reviewed on February 24, 2014. | This article was last modified on February 24, 2014.
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