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  Back Blood-tests Explained


Hepatitis A


At a Glance

Why Get Tested?

To help diagnose the cause of acute hepatitis; as part of a viral hepatitis panel to identify the type of hepatitis virus causing an infection; sometimes to evaluate the need for the hepatitis A vaccine

When to Get Tested?

When you have symptoms of an acute hepatitis infection, such as jaundice, or when you may have been exposed to hepatitis A virus (HAV)

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Hepatitis A is a highly contagious liver infection caused by the(HAV)virushepatitis A .It is one of several various causes of hepatitis, a condition characterized by inflammation and enlargement of the liver. This test detects antibodies in the blood that are produced by the immune system in response to a hepatitis A infection.

Hepatitis A is one of five "hepatitis viruses" identified so far, including B, C, D, and E, that are known to cause the disease. While hepatitis A can cause a severe, acute disease that typically lasts 1 to 2 months, it does not cause a chronic infection as do some of the other hepatitis viruses.

Hepatitis A is spread, most commonly, from person-to person through stool (fecal) contamination or by ingesting food or water contaminated by the stool of an infected person (a foodborne illness). Recognized risk factors for hepatitis A include close contact with an infected person, international travel, household or personal contact with a child who attends a child care center, household or personal contact with a newly arriving international adoptee, a recognized foodborne outbreak, men who have sex with men, and use of illegal drugs.

Although there are many causes of hepatitis, the symptoms remain the same. In hepatitis, the liver is damaged and unable to function normally. It cannot process toxins or waste products such as bilirubin for their removal from the body. During the course of the disease, bilirubin and liver enzyme levels in the blood can increase.While tests such as bilirubin or a liver panel can tell a health practitioner that someone has hepatitis, they do not identify the cause. Antibody tests for hepatitis viruses may help determine the cause.

There are two different classes of hepatitis A antibody that may be tested, IgM and IgG. When a person is exposed to hepatitis A, the body first produces hepatitis A IgM antibodies. These antibodies typically develop 2 to 3 weeks after first being infected (and are detectable before the onset of symptoms) and persist for about 3 to 6 months. Hepatitis A IgG antibodies are produced within 1 to 2 weeks of the IgM antibodies and usually persist for life.

  • Because hepatitis A IgM antibodies develop early in the course of infection, a positive hepatitis A IgM test is usually considered diagnostic for a current or recent infection of hepatitis A. This test may be done as part of an acute viral hepatitis panel used to determine which virus is causing symptoms when viral hepatitis is suspected.
  • An HAV IgG test may be used to help determine if a person has been infected in the past and has some immunity to the disease.
  • A total hepatitis A antibody test detects the presence of both the IgM and IgG antibodies, thus can identify current and past infections.

A vaccine that prevents hepatitis A has been available since 1995. Historically, infection rates varied cyclically, with nationwide increases every 10-15 years. However, rates have declined in general since the vaccine was introduced. In 2010, the number of acute hepatitis A cases reported nationwide declined by approximately 53% from about 3,600 in 2006.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

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.

When is it ordered?

Testing for the presence of IgM antibodies to hepatitis A is ordered when someone has acute symptoms such as:

  • Fever
  • Fatigue
  • Loss of appetite
  • Nausea, vomiting, abdominal pain
  • Dark urine and/or pale colored stool
  • Joint pain
  • Jaundice

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.

What does the test result mean?

Results of hepatitis testing may indicate the following:

HAV IgM HAV IgG or Total Antibody (IgM and IgG) Results Indicate
Positive Not Performed Acute or recent HAV infection
Negative Positive No active infection but previous HAV exposure; has developed immunity to HAV or recently vaccinated for HAV
Not Performed Positive Has been exposed to HAV but does not rule out acute infection
Not Performed Negative 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.

Is there anything else I should know?

Hepatitis A vaccines are effective even when administered up to 15 days after exposure to the virus. Infants, immunocompromised people, people with chronic liver disease, or adults over 40 may be given an injection of immune globulin instead of the vaccine for post-exposure protection.

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.



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