Hepatitis A cannot be differentiated from other types of viral hepatitis on the basis of clinical or epidemiological features alone. Appropriate blood tests must be used.
- Anti-HAV: Total antibody to HAV. This diagnostic test detects total antibody of both IgG and IgM subclasses of HAV. If positive, it indicates either acute or resolved infection.
- IgG anti-HAV: IgG antibody is a subclass of anti-HAV. It appears early in the course of infection, remains detectable for the person’s lifetime and provides lifelong protection against disease. Its presence indicates immunity through either HAV infection or HepA vaccination.
- IgM anti-HAV: IgM antibody is a subclass of anti-HAV. Its presence indicates a recent infection with HAV (6 months or less). It is used to diagnose acute (recently acquired) hepatitis A. Because of the risk of false positive IgM anti-HAV results, people should only be tested for IgM anti-HAV if they are symptomatic and suspected of having acute hepatitis A illness.
- HAV RNA tests also may be used to diagnose acute infection through the direct detection of viral RNA in serum or stool.
Total anti-HAV, which appears early in the course of infection, remains detectable for the person’s lifetime and indicates lifelong protection against the infection/disease. To confirm a diagnosis of acute HAV infection, serologic testing for IgM anti-HAV is required. In the majority of persons, serum IgM anti-HAV becomes detectable 5 to 10 days before onset of symptoms and lasts about 6 months. However, there have been reports of persons who test positive for IgM anti-HAV for up to a year or more following infection. An educational program on the interpretation of hepatitis A serology is available on the CDC website at www.cdc.gov/hepatitis/resources/professionals/training/serology/training.htm.