HIV testing: What tests and when to get tested

(MayoClinic.com) You may be thinking about getting tested for HIV for any number of reasons. Perhaps you've been exposed to someone's blood or had unprotected sex. Or maybe you just want to make sure. If you're considering HIV testing, you might be feeling some anxiety about it. Knowing what to expect from HIV testing and what types of tests are available can help.

If you do have HIV, the sooner you find out, the better. Early medical treatment and a healthy lifestyle may delay the onset of AIDS — a chronic, life-threatening condition caused by HIV.

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 to 64
• Pregnant, because if you're infected with HIV there are ways to reduce the chance you'll pass it along 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 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

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.

HIV is usually diagnosed by testing your blood or oral mucus 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 — usually two to eight weeks. In rare cases, it can take up to six months for HIV antibodies to develop and for these types of HIV tests to be accurate. However, the majority of tests are considered to be accurate within three months. A few early detection tests also exist, but they may be more costly and less widely available.

Traditional 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 — the same test is repeated. 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, and you receive a diagnosis of HIV only if all three tests are positive.

It can take up to two weeks to get the results of the ELISA and Western blot 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. The greatest disadvantage is that you're not offered the counseling that you typically receive in a clinic or doctor's office, although you're given referrals to medical and 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 ago.
• 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.

Can you test negative for HIV and still have HIV?
Yes. 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 more 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.

What if you test positive for HIV?
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. Inform any partners about a positive diagnosis, 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 STDs. You may have TB or STDs 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 to getting other STDs that may harm your health. But if you decide to have sex, use condoms. Condoms are very effective at preventing HIV and other STD transmission, though they aren't 100 percent effective.

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