Clinical and Interpretive

This test is used in the diagnosis of acute or recent hepatitis A infection.

Hepatitis A virus (HAV) is endemic throughout the world, occurring most commonly, however, in areas of poor hygiene and low socioeconomic conditions. The virus is transmitted primarily by the fecal-oral route, and it is spread by close person-to-person contact and by food- and water-borne epidemics. Outbreaks frequently occur in overcrowded situations and in high-density institutions and centers, such as prisons and health care or day care centers. Viral spread by parenteral routes (eg, exposure to blood) is possible but rare, because infected individuals are viremic for a short period of time (usually <3 weeks). There is little or no evidence of transplacental transmission from mother to fetus or transmission to newborn during delivery.

Serological diagnosis of acute viral hepatitis A depends on the detection of specific anti-HAV IgM. Its presence in the patient’s serum indicates a recent exposure to HAV. Anti-HAV IgM becomes detectable in the blood within 2 weeks after infection, persisting at elevated levels for about 2 months before declining to undetectable levels by 6 months. However, sensitive immunoassays may occasionally detect anti-HAV IgM for up to 1 year after acute hepatitis A.

A positive result indicates acute or recent (<6 months) hepatitis A infection. As required by laws in almost all states, positive antihepatitis A virus (anti-HAV) IgM test results must be urgently reported to state health departments for epidemiologic investigations of possible outbreak transmission.

A negative result may indicate either 1) inadequate or delayed HAV IgM response after known exposure to HAV, or 2) absence of acute or recent hepatitis A.

Borderline anti-HAV IgM test results may be seen in: 1) early acute hepatitis A associated with rising antibody levels, 2) recent hepatitis A associated with declining levels, or 3) cross-reactivity with nonspecific antibodies (ie, false-positive results). Retesting of both anti-HAV IgM and anti-HAV total in 2 to 4 weeks is recommended to determine the definitive HAV infection status.

False-positive test results may be due to presence of cross-reactive antibodies from other viral infection or underlying illnesses. Positive results should be correlated with the patient’s clinical history and epidemiologic exposure. Testing too early (<2 weeks) after exposure to hepatitis A virus (HAV) may yield negative anti-HAV IgM test results.

This test is not useful for determining presence of immunity to HAV infection from either past hepatitis A or vaccination against HAV.

Biotin may interfere with testing.