Polymerase chain reaction (PCR) testing, which is much more expensive
than AIDS antibody tests, should be used routinely to detect HIV
infection in infants but not in adults, according to two new studies
from Veterans Affairs and Stanford researchers.
"We found that PCR is not as accurate as antibody tests in
adults, but in infants it's one of the best tests available,"
said Dr. Douglas Owens, health services senior research associate
at the Veterans Affairs Palo Alto Health Care System and assistant
professor of medicine and of health research and policy at Stanford
University School of Medicine.
Researchers led by Owens and Dr. Mark Holodniy reported their
findings in the May 1 issues of the Annals of Internal Medicine
and the Journal of the American Medical Association. They
based their conclusions on analyses of 96 studies that evaluated
PCR screening for HIV in adults and 32 studies looking at the
technique in infants.
Unlike antibody tests, which detect molecules formed by the immune
system in response to HIV, PCR is a newer method that detects
viral genes in a blood sample. Within hours, this technique can
turn a tiny shred of genetic material into millions of easily
Method's Worth Has Been Debated
When PCR became available about 10 years ago, Owens said, many
physicians hoped it could be a useful test for HIV infection in
both infants and adults--despite its expense. Since then, the
method has become controversial, as numerous studies have failed
to agree on its value in HIV testing. "Some studies indicated
PCR testing was perfect, while others indicated it was inaccurate,"
To help settle the issue, Owens and his colleagues performed a
meta-analysis on data from a number of smaller studies. The researchers
concluded that antibody tests are more accurate than PCR in adults
and recommended adult PCR testing in only a few situations. For
example, PCR may help detect HIV in people exposed so recently
that their bodies haven't yet generated antibodies against the
For infants, however, the researchers concluded that PCR is very
useful in diagnosing HIV infection. All babies born to mothers
with HIV have maternal antibodies against the virus in their blood
for about 15 to 18 months, and therefore, antibody tests cannot
tell physicians whether a newborn is actually infected, Owens
Although PCR is one of the most accurate tests for use in infants,
he said, a single test result is not sufficient to make or exclude
the diagnosis. Rather, doctors should follow the infant closely
for signs of HIV infection.
PCR Accuracy Depends Partly on Age
The accuracy of PCR depends, in part, on the child's age, Owens
explained. "Current thinking is that a baby often is infected
during birth, and it takes a while for the numbers of virus to
build," he said. The researchers recommend using PCR after
a child is 30 days old or repeating the test if it is used in
In addition to Owens and Holodniy, who directs the AIDS research
center at the Palo Alto VA, coauthors of the JAMA report on adult
studies were Dr. Thomas McDonald, John Scott, and Seema Sonnad.
The Annals coauthors, along with Owens, Holodniy, Scott,
and Sonnad, were Dr. Alan Garber, Lincoln Moses, Dr. Bruce Kinosian,
and Dr. J. Sanford Schwartz.
The research was supported by the U.S. Department of Veterans
Affairs and the National Institutes of Health.