Reuters Health Information (2005-05-12): False-positive results common in acute hepatitis A testing
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
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
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.