Hepatitis A tests come in a variety of forms. Formally, viral hepatitis A antibody tests are instituted to diagnose liver infection caused by the virus. There are two different versions of hepatitis A tests which test for two different antibodies that are associated with hepatitis A infection: the HAV- Ab lgM, and the HAV-Ab Total. The tests can be used to detect an acute infection of the virus, a past infection of the virus, or immunity from the virus. During a test that detects acute infection, other complementary screenings may be done, including a liver panel and a bilirubin test.
The test that is done when acute hepatitis symptoms are present is the HAV-Ab lgM. When the body is first exposed to hepatitis A, lgM is the first antibody that is produced to fight the infection. This is the favorite choice of the two hepatitis A tests because it can be given rapidly if the patient presents with acute liver infection signs including feverish stomach flu-like symptoms, dark urine and abnormal stool, or jaundice. Even if the severity of symptoms is relatively low, the HAV-Ab lgM test can be given to patients believed to have been recently exposed. Since the virus is spread easily through contaminated fecal matter, young children may be routinely tested if they are ill with symptoms that resemble those associated with hepatitis A.
The second of the two hepatitis A tests is the HAV-Ab Total. This test screens for the lgM antibody as well as a second antibody produced by the body in response to hepatitis A infection, lgG. There is not a single test available to test for the lgG antibody alone, so it is tested in conjunction with lgM. The lgG antibodies develop at a later stage in the infection, and they may remain present in the body for many years and sometimes for the lifetime of the person that has been exposed.
Of the two hepatitis A tests, the HAV-Ab Total is more thorough, as it detects acute and past infections with the hepatitis A virus. If the doctor has any question as to whether the patient has been exposed to hepatitis A in the past, this is the test usually given. Aside from detecting a possible active infection, this test can tell the physician whether a vaccination against hepatitis A is appropriate. After a person has been exposed to the virus, an adequate immunity is often built, and the patient may not need a vaccination against the virus. If the HAV-Ab Total test comes back negative and a vaccination is given, the test may be given again to see if adequate antibodies have been produced.