How HIV Tests Work: What to Know Before You Get One

These tests detect HIV within weeks of exposure.

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For decades, testing for HIV, or human immunodeficiency virus, was much more rudimentary than it is now. The HIV tests available today have progressed and become more effective, according to hematologist Jeffrey Laurence, MD, of Weill Cornell Medicine in New York City.

The earliest HIV test came into use in April 1985. This simple test, known as the Elisa test, checked for antibodies against HIV in the blood. The immune system creates these antibodies in response to infections like HIV, so the presence of antibodies is a sign of HIV infection. Although groundbreaking at the time, the Elisa test had a high false-positive rate, so follow-up tests were always necessary.

Tests for HIV are far more sensitive today, says Dr. Laurence, who has authored more than 150 scientific papers related to AIDS. These newer combination, or fourth-generation, tests check for both antibodies and antigens—the foreign substances that come from the virus—and can detect an HIV infection around three to four weeks after exposure.

Another type of HIV test looks directly for the genetic material of the HIV virus in the blood, not only for the antibodies and antigens. The nucleic acid test (NAT) can detect HIV infection as early as two to seven days after transmission. However, the NAT is pricey, so this test is often only used for high-risk exposure, such as a health care worker who suspects they may have been exposed.

For a needle-free test, someone can also purchase a home HIV testing kit. These DIY tests use an oral swab that you do in your own home and then mail back to the company for testing. While home testing for HIV is a convenient option, Dr. Laurence still recommends making an appointment with a doctor or clinic. Depending on the test results, the patient can more easily have a conversation about immediate treatment options (if the HIV test results come back positive) or counseling on preventing HIV in the future (if negative).

Looking for more information about HIV testing? Here are the guidelines on who should be tested for HIV.