Testing, Testing, One, Two, Three: How HIV Tests Work

HIV hasn't disappeared. The numbers are still haunting. Half of all new HIV infections occur in people under the age of 25. This equates with 2 new infections every hour of every day in this population. The good news is that early detection of the disease will make treatment more successful, and testing is a relatively easy and cheap (often free) process. By testing yourself now, you not only help yourself, you also protect those around you from becoming infected.

Should I Get Tested? In a lecture on AIDS, an infectious disease specialist was asked how he determined whether to test a patient for HIV. The specialist replied, "My policy is, if they have a sexual organ, I test "em." In other words, everyone who has sex is at risk of getting HIV.

You should consider getting tested if you:

  • Are sexually active, regardless of your sexual orientation or number of partners
  • Have ever used intravenous drugs or shared needles
  • Have ever had a blood transfusion, particularly if it was before 1985
  • Are pregnant

If you are in a "monogamous" relationship, how certain are you that your partner is truly monogamous? How certain are you that your partner had not already contracted HIV by the time you met each other? A popular myth is that you can tell which people have HIV by how they look. If they had it, they would look ill, right? Wrong. People can be completely healthy for years before developing any symptoms of HIV-related illness.

Because HIV is most easily contracted by direct blood-to-blood contact, you can get HIV by having had a blood transfusion or using intravenous (IV) drugs. Due to strict screening, the risk of contracting HIV from a unit of donated blood is currently estimated to be in the neighborhood of 1 in 500,000. Transfusions performed in the 1970s and 1980s, however, carried a much higher risk. Sharing needles during IV drug use is a very significant risk factor. If you've had a transfusion in the past, or if you use IV drugs, you are a candidate for testing.

In the words of a medical school professor, "pregnancy is a sexually transmitted disease." This tongue-in-cheek statement is nevertheless accurate, since pregnancy is sexually transmitted -- as is HIV. If you are pregnant, it means that you have had unsafe sex, and are therefore at risk for having contracted HIV. Furthermore, up to 33 percent of HIV-positive women end up transmitting HIV to their baby. With medication, though, the risk of transmitting HIV to your baby can be reduced to 8 percent or less. If you are pregnant, getting an HIV test not only helps you -- it could save your baby from contracting HIV.

What is the HIV Test? The standard HIV antibody test (called an ELISA) is a blood test that doesn't actually detect HIV, but detects your immune system's response to the virus. When your body is infected by a virus (or anything else), special white blood cells make proteins called antibodies to help neutralize and attack the infecting agent. Even though antibodies cannot protect you from HIV, they are useful in making the virus's presence known.

HIV-antibody test results usually come back in about a week. If the test is positive, which means antibodies were detected, then a more accurate test called a Western Blot is performed. This test looks for actual evidence of HIV, not just antibodies. Combined, the HIV antibody test and the Western Blot test can detect HIV in more than 99.5 percent of those infected. If both these tests are positive, most patients then undergo a polymerase chain reaction (PCR) assay, which determines the actual level of HIV in the blood. Although the PCR test gives the quickest result, it is so sensitive that it often gives a false positive result. Considering its sensitivity and high cost, the PCR test is not considered an effective routine screening test for HIV.

Are There Flaws in the HIV Test? Yes. Since your body may take anywhere from weeks to months to make antibodies after HIV infection, there is a "window" of time when the antibody test will give a false negative result. This means you may actually have HIV, but the test says you don't. To be on the safe side, we say that the HIV test has a six-month window to be false negative. So, to ensure that you are HIV-negative now, you'll need to repeat the test in six months to a year from now. A negative test result basically means only that you were HIV-negative six months ago. If during that time you continue to be at risk for contracting the virus, you'll have to get tested yet again. Unless you are abstinent or in a monogamous relationship (and you should always be skeptical) you should probably get tested for HIV at least once every few years.

Current evidence indicates that if HIV infection is more advanced before treatment is begun, therapy is less likely to be successful than it would be had the HIV infection been caught earlier on. Therefore, one of the keys to successful treatment is starting early. Don't wait. Get tested now.

For a testing or treatment center, contact: National AIDS Hotline (800) 342-AIDS (2437)

HIV/AIDS Treatment Information Service (800) 448-0440