Testing for hepatitis A infection should be reserved for patients who have symptoms consistent with the diagnosis or who have had recent exposure to a person known to be infected with hepatitis A, the Centers for Disease Control and Prevention said.
Specifically, IgM anti-hepatitis A virus (HAV) testing should not be done routinely to screen people who have liver function test abnormalities or who are suspected of having hepatitis C, the CDC said (MMWR 2005;54:453–6).
After receiving multiple reports of positive IgM anti-HAV test results in individuals who did not have clinical illness consistent with HAV infection, the CDC investigated the clinical and epidemiologic characteristics of these cases for the first time. The CDC's findings suggest that these people are unlikely to have the illness unless they have been exposed recently to someone with acute HAV infection. The findings also indicate that their contacts are unlikely to require immunoprophylaxis. Therefore, testing these individuals only serves to lower the predictive value of the IgM anti-HAV test.
In Connecticut, the state health department investigated 127 positive IgM anti-HAV test results; 108 of the individuals had clinical illness consistent with hepatitis A infection. Of the other 19 persons (aged 28–88 years), 3 had elevated alanine aminotransferase (ALT) concentrations and 3 had a previous report of a positive IgM anti-HAV test but did not have illness that met the case definition at that time either.
Among 10 such people in Alaska (aged 9–77 years), 7 had abnormal ALT concentrations, suggesting the presence of liver injury or disease. However, six did not have an illness with acute onset, while the seventh had an acute illness traced to acetaminophen toxicity. The other three were asymptomatic. One person previously had a positive IgM anti-HAV test.
In a third investigation involving six U.S. counties with demographic compositions representative of the U.S. population, 140 persons were reported to have a positive IgM anti-HAV test result. Of those, 62% (87) did not have an illness consistent with the case definition, while 38% (53) did.
The 87 persons who did not have illness meeting the case definition were significantly older and more likely to be female (this was also the case in Connecticut). Of 31 for whom serum samples were available for repeat testing at the CDC, only 2 tested positive for IgM anti-HAV. Of 25 specimens tested for HAV nucleic acid, only 1 (4%), from a 77-year-old man, had detectable HAV RNA. In contrast, 34 of 51 specimens from persons with both clinical and laboratory evidence of HAV infection had detectable HAV RNA.
A repeat test of the 77-year-old man's specimen was negative for IgM anti-HAV, suggesting that his RNA test was a false positive, the CDC said.
A positive IgM anti-HAV test in a person without typical symptoms of hepatitis A infection might indicate asymptomatic acute HAV infection, previous HAV infection with prolonged presence of IgM anti-HAV, or a false-positive result. The findings from these reports suggest that in older adults, the most likely explanations are a false-positive result or a HAV infection that occurred months to years previously, rather than more recent infection requiring consideration of postexposure immunoprophylaxis for contacts.
Published guidelines for the work-up of abnormal liver enzyme tests do not include IgM anti-HAV testing, yet physicians may be tempted to order a multitest “hepatitis panel” offered by some laboratories at a cheaper price than the individual tests, James Hadler, M.D., state epidemiologist in the Connecticut Department of Public Health in Hartford, told this newspaper.
“It is this kind of reflex bargain basement testing that may result in getting back false-positive results,” Dr. Hadler said.
HAV infection causes an acute illness with discrete onset of fatigue, abdominal pain, loss of appetite, intermittent nausea and/or vomiting, and jaundice or elevated serum alanine aminotransferase levels.