Two Studies Conclude That PCR Testing for HIV is Warranted in Infants but Not Adults

Polymerase chain reaction (PCR) testing, which is much more expensivethan AIDS antibody tests, should be used routinely to detect HIVinfection in infants but not in adults, according to two new studiesfrom Veterans Affairs and Stanford researchers.

"We found that PCR is not as accurate as antibody tests inadults, but in infants it's one of the best tests available,"said Dr. Douglas Owens, health services senior research associateat the Veterans Affairs Palo Alto Health Care System and assistantprofessor of medicine and of health research and policy at StanfordUniversity School of Medicine.

Researchers led by Owens and Dr. Mark Holodniy reported theirfindings in the May 1 issues of the Annals of Internal Medicineand the Journal of the American Medical Association. Theybased their conclusions on analyses of 96 studies that evaluatedPCR screening for HIV in adults and 32 studies looking at thetechnique in infants.

Unlike antibody tests, which detect molecules formed by the immunesystem in response to HIV, PCR is a newer method that detectsviral genes in a blood sample. Within hours, this technique canturn a tiny shred of genetic material into millions of easilyanalyzed copies.

Method's Worth Has Been Debated

When PCR became available about 10 years ago, Owens said, manyphysicians hoped it could be a useful test for HIV infection inboth infants and adults--despite its expense. Since then, themethod has become controversial, as numerous studies have failedto agree on its value in HIV testing. "Some studies indicatedPCR testing was perfect, while others indicated it was inaccurate,"Owens noted.

To help settle the issue, Owens and his colleagues performed ameta-analysis on data from a number of smaller studies. The researchersconcluded that antibody tests are more accurate than PCR in adultsand recommended adult PCR testing in only a few situations. Forexample, PCR may help detect HIV in people exposed so recentlythat their bodies haven't yet generated antibodies against thevirus.

For infants, however, the researchers concluded that PCR is veryuseful in diagnosing HIV infection. All babies born to motherswith HIV have maternal antibodies against the virus in their bloodfor about 15 to 18 months, and therefore, antibody tests cannottell physicians whether a newborn is actually infected, Owensnoted.

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 excludethe diagnosis. Rather, doctors should follow the infant closelyfor signs of HIV infection.

PCR Accuracy Depends Partly on Age

The accuracy of PCR depends, in part, on the child's age, Owensexplained. "Current thinking is that a baby often is infectedduring birth, and it takes a while for the numbers of virus tobuild," he said. The researchers recommend using PCR aftera child is 30 days old or repeating the test if it is used innewborns.

In addition to Owens and Holodniy, who directs the AIDS researchcenter at the Palo Alto VA, coauthors of the JAMA report on adultstudies 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 VeteransAffairs and the National Institutes of Health.