Public Health

False-positive results common in acute hepatitis A testing

Last Updated: 2005-05-12 14:17:40 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Routinely testing patients who do not have clinical symptoms of hepatitis A virus (HAV) infection or a history of exposure raises the likelihood of obtaining false-positive results, investigators report in the Morbidity and Mortality Weekly Report for May 13th.

"To improve the predictive value of a positive IgM anti-HAV test, clinicians should limit laboratory testing for acute HAV infection to persons with clinical findings typical of hepatitis A or to persons who have been exposed to settings where HAV transmission is suspected," lead author Dr. Z. F. Dembek, at the Connecticut Department of Public Health, and colleagues note.

Dr. Dembek's group investigated cases that tested positive for IgM anti-HAV in Connecticut and Alaska, and also review data from the 2003 Sentinel Counties Study.

In Connecticut, 127 positive test results were reported between 2002 and 2003, but only 108 of the patients had illness consistent with acute HAV. Of the remaining 19 considered to be false-positives, 9 were asymptomatic and 10 had clinical presentations that were not consistent with HAV.

In Alaska, there were 27 cases consistent with HAV reported to the Alaska Division of Public Health between 2002 and 2004, as well as 10 apparent false positives. Of these 10, seven patients had elevated serum alanine aminotransferase (ALT) levels and the other three were asymptomatic.

In the Sentinel Counties Study conducted in six US counties, CDC researchers found that, of 140 persons with positive IgM anti-HAV test results, only 53 (38%) had illness consistent with the case definition. HAV RNA was detected in one of 25 (4%) subjects not meeting the case definition, compared with 34 (66%) of those with apparent HAV illness.

In all three data sets, most false-positives came from older adults without typical risk factors for infection. In fact, most who underwent retesting had negative results.

"The use of IgM anti-HAV as a screening tool or as part of testing panels used in the workup of nonacute liver function abnormalities should be discouraged," editorialists write.

They add that clinicians making decisions about postexposure immunoprophylaxis among contacts of those testing positive for IgM anti-HAV, but in whom clinical illness and exposure history are absent, should seek additional information.

MMWR 2005;54:453-456.