HIV antibody tests unreliable for early infections in teens

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Jun 21 2009

A previously healthy teenager shows up at the doctor's office with a sore throat, fever, aches and general malaise. Routine blood tests are normal, an HIV test comes back negative, and the pediatrician sends the patient home with a diagnosis of acute viral infection.

Two weeks later, the teen returns complaining of lingering symptoms and persistent high fevers. This time, a repeat HIV test comes back positive. What happened?

The most commonly used rapid HIV test resulted in a false negative the first time around, which happens quite often during the earliest - and most contagious - stages of HIV infection, known as acute retroviral syndrome (ARS), explains Allison Agwu, M.D., a pediatric infectious disease specialist at Johns Hopkins Children's Center.

Because the rapid HIV screening tests are designed to detect antibodies to the virus, not the virus itself, such tests will only pick up infection in those who have developed antibodies, which most people don't make until several weeks to several months after infection.

Agwu cautions that "if a teen engages in risky behaviors and has symptoms of flu or mononucleosis, pediatricians should look further and not be lulled into a false sense of security by a negative rapid HIV test."

Because an estimated 14 teenagers become infected with HIV every day in the United States, because ARS is both under-reported and underdiagnosed and because early infections are highly contagious, ARS should be on every pediatrician's radar screen, Agwu says.

To rule out HIV in teens deemed to be at high risk for sexually transmitted infections, Hopkins HIV experts recommend the use of polymerase chain reaction (PCR) tests, which directly detect the virus' genetic markers, rather than antibodies to the virus.

PCR tests, while more expensive than standard antibody tests, can detect the virus within two to three weeks after it enters the body.

"Am I suggesting that every teen with flu-like symptoms should get a PCR? No. But I am suggesting that pediatricians take an extra minute to ask probing questions about risk behaviors and exposures in the last two months," Agwu says. "If the answers make you suspicious, then order the PCR."

Consider ordering a PCR test if the patient is sexually active or has used injectible drugs and has two or more of the following symptoms: