HIV testing

Definition

Human immunodeficiency virus (HIV) testing determines whether or not you're infected with HIV, a virus that weakens your immune system and can lead to acquired immunodeficiency syndrome (AIDS).

You may think about HIV testing if you've been exposed to blood or had unprotected sex. Or maybe you just want to make sure. Regardless of your reason for getting tested, HIV testing is likely to make you anxious. Knowing what to expect from HIV testing and what types of tests are available can help.

Why it's done

HIV testing is essential for slowing the spread of HIV infection. Once you're infected, HIV slowly but systematically attacks your immune system. During this latent phase of infection, many people assume they're healthy and continue to have unprotected sex or share needles — and transmit the virus to others.

If you get tested and find out you're HIV positive, you can also start medical treatment before your immune system is severely damaged. Early HIV treatment may delay the progression to AIDS.

If you think you may have HIV — get tested. The Centers for Disease Control and Prevention (CDC) encourages voluntary HIV testing as a routine part of medical care if you are:

• An adolescent or adult between the ages of 13 and 64
• Pregnant, because if you're infected with HIV there are ways to reduce the chance you'll pass it along to your baby

Testing for pregnant women, in particular, is especially important because HIV-positive mothers can pass HIV on to their babies during pregnancy or delivery or through breast-feeding. Taking anti-retroviral medication during pregnancy and delivery greatly reduces the risk that you'll pass HIV on to your baby.

Yearly testing is recommended if you're at high risk of infection. Consider HIV testing yearly and before having sex with a new partner if you:

• Have had unprotected vaginal, oral or anal sex with more than one sexual partner or with an anonymous partner since your last screening
• Are a man who has sex with men
• Use intravenous (IV) drugs
• Have been diagnosed with tuberculosis or a sexually transmitted disease (STD) such as hepatitis or syphilis
• Have had unprotected sex with someone who falls into any of the above categories

How you prepare

No special preparations are necessary for HIV testing. You may need to call your doctor to schedule an appointment. Some public health clinics may allow you to simply walk in for HIV testing.

What you can expect

HIV is usually diagnosed by testing your blood or a sample of cells taken with a cotton swab from inside your cheek for the presence of antibodies to the virus.

Unfortunately, these HIV tests aren't accurate immediately after infection because it takes time for your body to produce antibodies to the virus. The presence of these antibodies indicates infection with HIV. Seroconversion, or the transition from HIV-negative (not infected) to HIV-positive (infected), usually takes two to eight weeks. Results are more reliable, however, if you wait three months after possible exposure to be tested. The interval between HIV exposure and seroconversion may stretch as long as six months, but that's unusual.

Standard HIV testing
The enzyme-linked immunosorbent assay (ELISA) test looks for antibodies to the virus in a sample of your blood drawn from a vein.

If this test is positive — meaning you have antibodies to HIV — lab technicians run the same test again on the sample you provided. If the repeat test is also positive for HIV antibodies, you need a confirming blood test called the Western blot test, which checks for the presence of HIV proteins. The Western blot test is important because you may have non-HIV antibodies that cause a false-positive result on the ELISA test. Combining the two types of tests helps ensure that results are accurate. You receive a diagnosis of HIV only if all three tests are positive. It can take a few days to a few weeks to get the results from all three tests.

Rapid HIV testing
Several rapid tests offer highly accurate information within as little as 20 minutes. These tests also look for antibodies to the virus using a sample of your blood, drawn from a vein or a finger prick, or fluids collected on a treated pad that's rubbed on your upper and lower gums. The oral test is almost as sensitive as the blood test and eliminates the need for drawing blood. A positive reaction on a rapid test requires a confirming blood test. And because the tests are relatively new and were originally approved for use only in certified laboratories, they may not be available everywhere.

Home HIV testing
Currently, the Food and Drug Administration (FDA) has approved only one HIV test for home use. The Home Access HIV-1 Test System, marketed by Home Access Health, is as accurate as traditional HIV tests, and all positive results are automatically retested.

For this test, you mail in a drop of your blood, then call a toll-free number to receive your results in three to seven business days. This approach ensures your privacy and anonymity — you're identified only by a code number that comes with your kit. You may speak to a counselor before taking the test, while you're waiting for results or after you've received your results. If you test positive, you're given referrals for follow-up testing and for social services.

Early detection HIV testing
Some tests can detect HIV infection earlier, before antibodies are detectable in standard HIV testing. These tests may cost more than standard HIV testing and may not be as widely available. You will also still need standard antibody testing later, to confirm results, because false-positives and false-negatives are possible. Tests that can help identify early HIV infection include:

• PCR or RNA tests. Polymerase chain reaction (PCR) tests involve evaluating a blood sample for genetic material — RNA or DNA — produced by the HIV virus infection. These tests measure the amount of virus present in your blood (viral load) and are most useful for monitoring your condition after you've already been diagnosed with HIV. The tests may return a false-negative result if infection with HIV occurred too recently, such as fewer than five days prior to the test.
• p24 antigen tests. This test can identify an HIV protein — p24 — in your blood from about one week to up to three or four weeks after infection with HIV. Once antibodies begin to form, they bind to the p24 protein, making p24 undetectable. By that time, standard antibody tests may be able to detect the antibodies.

Results

Negative HIV test results
A negative test result from HIV testing may mean one of two things: You don't have HIV, or it's too soon yet to tell.

If you were only recently exposed to the HIV virus, you could test negative and still have HIV (false-negative), particularly with the standard antibody tests. Unfortunately, you may also be at greatest risk of spreading the virus during this time.

If you test negative for HIV during standard antibody HIV testing and it's been less than three months since the suspected exposure, consider retesting. The best time for retesting is three months or longer after the possible exposure.

Instead of waiting to be retested with an antibody test, you may also have the option of getting one of the few less commonly done tests that can identify HIV infection earlier, before antibodies can be detected.

Positive HIV test results
Although there's no cure for HIV/AIDS, treatment has come a long way in the past few decades, offering extended and improved quality of life for many. Early treatment can help you stay well and delay the onset of AIDS. Tell your partners if you test positive for HIV, because they will need to be evaluated and possibly treated, as well.

Discuss further testing and treatment with your doctor. Your doctor will use PCR tests to measure the amount of the virus in your blood, which can help predict the probable progression of your disease. People with higher viral loads generally don't do as well as those with lower viral loads. Viral load tests are also used to decide when to start and when to change your treatment.

A healthy lifestyle can also help you stay well:

• Avoid smoking, using illicit drugs and drinking too much alcohol. These can weaken your immune system.
• Get tested for tuberculosis (TB) and sexually transmitted diseases (STDs). You may have TB or a sexually transmitted disease (STD) and not know it. These may cause serious illness if not treated.
• Use condoms. Abstaining from sex is the most effective way to avoid transmitting HIV to others or getting other STDs that may harm your health. But if you decide to have sex, use approved condoms correctly. Condoms are very effective at preventing HIV and other STD transmission, though they aren't 100 percent effective.