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Hepatitis A Virus Antibody IgM

The hepatitis A virus (HAV) is a small, 27 nm RNA virus. It is transmitted primarily by the fecal-oral route, and is found more commonly in situations where unsanitary conditions and/or close contact among individuals exist. Contaminated food and water are frequent means of transmission. Although ~70% of children aged <6 years with HAV infection are asymptomatic, older children and adults usually have symptoms and 70% are jaundiced.

The incubation period is short, averaging 25 days and ranging from 15-45 days. Serum IgM antibody to the hepatitis A virus (anti-HAV) appears at about four weeks after initial infection and usually persists for 2-6 months as the initial phase of the immune response. Subsequently, only IgG antibodies are detected. Serum IgG antibody to HAV generally persists for lifetime, conferring immunity to further type A infection. HAV is typically self-limited and does not lead to chronic liver disease or to a persistent carrier state.

Measurement of the HAV IgM antibody is the preferred diagnostic test for acute infection. A positive IgM anti-HAV test result in a person without symptoms of hepatitis A might indicate:

  • Asymptomatic acute HAV infection
  • Previous hepatitis A infection with prolonged presence of IgM anti-HAV
  • False positive test result
A minority of patients have detectable IgM anti-HAV for as long as 30 months after onset of illness. False positive results are more likely to occur when patients are tested who do not have symptoms of acute hepatitis. False positive results also are more likely to be female and older. A false positive result is likely if a patient has a positive IgM anti-HAV and a negative total (IgG and IgM) anti-HAV result.

Results are reported as positive or negative. Reference value is negative.

Specimen requirement is one SST tube of blood.

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