HIV testing, also called HIV screening, is the only way to know if you have the virus. Several types of tests check your blood or other body fluids to see whether you're infected. Most can't spot HIV right away because it takes time for your body to make antibodies or for enough of the virus to grow inside you. If you have the virus, finding out quickly means you can start treatment right away so you can feel better and live a long, full life. You can also take steps so you don't pass HIV to other people. Pregnant women should get tested because early treatment means you probably won’t pass it to your baby. The CDC recommends that everyone in the United States between the ages of 13 and 64 get tested for HIV at least once. You should be tested more often -- at least once a year -- if you’re at higher risk of getting HIV, including if you:
There are two basic ways to get HIV test results: Laboratory tests. For these tests, a technician takes a sample of your blood and tests it. You’ll get results within a few days. Rapid tests. These tests provide results in about 20-30 minutes. You can get them done in a community clinic or take them at home. If you’ve had a high-risk exposure to HIV very recently, go to the emergency room or call your doctor right away. Examples include unsafe sex with someone who has HIV or if you were sexually assaulted. Emergency drugs called post-exposure prophylaxis (PEP) may prevent HIV infection. You need to take them within 72 hours (3 days) after exposure. The sooner you start, the better. If you don't get to a doctor in time to get PEP, ask your doctor about getting tested for HIV. For most types of HIV tests, you’ll need to wait 2 weeks or more after exposure to get an accurate result. You can infect others soon after you're exposed, so practice safe sex and take other precautions in the meantime. Almost everyone who is HIV-positive has detectable levels of antibodies at 3 months. So if you test negative a month or two after your exposure, your doctor may want you to retest after 3 months to be sure. Every HIV test has a different “window period.” That’s how long you need to wait after exposure until you can expect an accurate result. No HIV test can tell if you have the virus just after you’ve been exposed. If you get tested too soon, you may get faulty results. But if you wait too long to learn if you’re HIV-positive, you can miss out on early treatment and also unknowingly spread the virus to others. Standard HIV blood test. This test uses blood that a technician takes from your vein and sends to a lab. It can find antibodies (proteins your immune system makes when you’ve been exposed to the virus) 23-90 days after infection. Rapid blood test. This test looks for antibodies using a drop of blood from a prick of your fingertip. It’s about as accurate as the original antibody test, but its window period could be longer -- between 18 and 90 days. Your health care provider can do this test, or you can buy a kit that lets you mail your sample in for testing. Antibody/antigen test. These tests look for both antibodies and an antigen, a substance the virus makes before your immune system can start making antibodies. An antibody/antigen test that uses blood taken from a vein can find HIV 18-45 days after you’re exposed to the virus. Newer antigen/antibody combination tests (you might hear them called “fourth generation” tests) can find HIV in 99% of people who are tested within 13-42 days of exposure. This test has become the standard HIV blood test in most labs. A rapid antibody/antigen can also be done using blood from a prick of your fingertip. A health care provider can do this test. Or you can use a mail-in kit. The window period for this test is 18 to 90 days. Rapid oral test. You can do this quick, easy test at home. Just rub a swab in the area between your gums and teeth to collect a sample of oral fluid (it isn’t the same as saliva) for antibodies against HIV. If you’ve had the virus for a while, the rapid oral test is highly accurate. But if you have a new infection, even if you got it in the past few months, the test won’t be as reliable. The window period is 23 to 90 days. Urine test. These also look for HIV antibodies, but they aren’t as accurate as other tests that check either your blood or oral fluid. Because it’s an antibody test, its window period is similar to that of a standard HIV test. Nucleic acid tests (NAT). These tests look for HIV at around 10-33 days after infection. They screen for signs of the virus itself, not antibodies to it. You may also hear this called an HIV RNA or a viral load test. It uses blood taken from a vein. You probably won’t get this expensive test unless you have symptoms and the doctor thinks you have a recent infection. It’s most often used to see how people who already have HIV respond to treatment. For a lab test, you might need to call your doctor to schedule it. Some public health- clinics take walk-ins. A technician will take a small blood sample and send it to a lab. Some immunoassay tests check your urine or fluids from your mouth (not saliva), but there aren't as many antibodies in these, so you may get false negatives. With home blood tests, you prick your finger to get a small blood sample that you send to a lab. You call to get your result, and you don't have to give your name. If it's positive, the lab will also do a follow-up test to double-check. With home oral fluid tests, you swab your upper and lower gums and test the sample in a vial. About 1 in 12 people who are infected get a false negative from this test. If it’s positive, get a lab test to confirm. How long does it take to get HIV results? This depends on what kind of test you had. Rapid tests provide answers in less than a half-hour. With a standard blood test or antibody/antigen test, you should expect results in a few days. It may take several days to get results from an NAT test. Urine test results could take up to 2 weeks. Some tests are anonymous, meaning your name isn’t tied to the result. Others are confidential: Your information is attached to the result, but it’s protected by privacy laws. Positive test results. A positive test result means there are traces of HIV in your body. Health care providers never diagnose HIV based on a single test result. If you had a rapid test, get a standard lab test to confirm it. If you had a lab test, more detailed tests of your blood can confirm your diagnosis:
A positive HIV test doesn’t mean you have AIDS, the most advanced stage of the disease. HIV treatment can keep you from getting AIDS, so talk to your doctor right away about starting medications called antiretroviral therapy (ART). These drugs lower the amount of the virus in your body, sometimes to a point where a test can’t spot it. They also protect your immune system so your HIV infection doesn’t become AIDS. False-positive test results. Some HIV tests have a very slight chance of giving you false results. A “false-positive” result means the test shows you have HIV when you don’t. This occasionally happens when your test detects antibodies but they’re antibodies to another infection or substance – not to HIV. Rarely, a false positive can result from a lab mix-up or misinterpretation. The rapid oral fluid test is more likely to give you a false-positive result than other tests. If you get a positive result on a rapid oral test, your doctor will give you a blood test to confirm your diagnosis. Negative test results. If your result is negative, you can take steps to protect yourself from HIV. They include practicing safe sex and taking medicine called pre-exposure prophylaxis (PrEP). Even if your test is negative, your partner can still have the virus. Talk with them about getting tested. It could take as long as 6 months for you to have enough antibodies to get a positive result on some tests. If it’s been 3 months or less since you might have been infected and your test result is negative, get another test at 6 months to be sure. False-negative test results. It’s also possible to get a “false-negative” result. That means the test says you don’t have HIV, but you do. This may happen if you get tested before or early in the window period for your particular test. It also sometimes happens in people taking antiretroviral medicine for PrEP or PEP. Otherwise, it’s very rare to get a false negative after the window period. Where you get tested for HIV depends on what’s available in your area, how much you can spend, and your preferences. Among the places that offer testing are:
Testing through local health departments and college health centers is often free. Some nonprofits also offer free or low-cost testing. If you test positive, these organizations can help you get treatment. If you test negative, they can tell you about ways to prevent HIV infection. At-home testing kits are available online and at pharmacies without a prescription. They generally offer you access to telephone counseling before and after testing. To find out where you can get tested, check hiv.gov or gettested.cdc.gov, or call 800-CDC-INFO (800-232-4636). Research has shown that some people avoid getting an HIV test because they fear others’ negative attitudes about HIV. This stigma results largely from fear, outdated beliefs about how HIV is transmitted, and value judgments about people who have it. People may think an HIV diagnosis could:
Other barriers to HIV testing include economic, cultural, and social issues such as:
And, of course, it’s common to be afraid of getting a positive test result. But learning your status can relieve the anxiety of uncertainty. If you don’t feel comfortable going to your regular doctor, consider testing by a nonprofit group or community health center. Some serve particular populations, such as LGBTQ+ people. They may even offer mobile testing vans. Or you may prefer to self-test in the privacy of your home. |
What are the two lab tests used to diagnose and confirm the presence of human immunodeficiency virus?
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