Types of HIV tests

Types of HIV tests

What Is HIV Testing?

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.

HIV testing determines if a person is infected with HIV. The human immunodeficiency virus (HIV) is the virus that causes acquired immunodeficiency syndrome (AIDS). AIDS is the most advanced stage of HIV infection.

Importance of HIV Testing for Prevention of HIV Infection. Knowing your HIV status
can help keep you and others safe.

If you are HIV negative:

People who get tested and a negative HIV test result shows that you do not have HIV. Continue taking steps also make decisions about sex, drug use, and health care that can protect them from HIV. For people at risk for HIV, such as using condoms during sex and, if you are at high risk of getting HIV, taking medicines to prevent HIV (called pre-exposure prophylaxis or PrEP) is highly effective for preventing HIV.

If you are HIV positive:

People who get tested and a positive HIV test result shows that you have HIV, but you can still take steps to protect your health. Begin by talking to your health care provider about antiretroviral therapy (ART). People on ART take a combination of HIV medicines every day to treat HIV infection. ART is recommended for everyone who has HIV, and people with HIV should start ART as soon as possible. ART cannot cure HIV, but HIV medicines help people with HIV live longer, healthier lives.

Studies show that the sooner people start treatment after diagnosis, the more they benefit from ART. Treatment with ART reduces the amount of HIV in the blood (called viral load), reduces HIV-related illness, and helps prevent transmission to others. People with HIV who take HIV medicine as prescribed and get and keep an undetectable viral load (or stay virally suppressed) have effectively no risk of transmitting HIV to HIV-negative sex partners.

Pregnant women should get tested because early treatment means you probably won’t pass it to your baby.

What kinds of tests are available, and how do they work?

HIV Tests for Screening and Diagnosis. HIV tests are very accurate, but no test can detect the virus immediately after infection. How soon a test can detect HIV depends upon different factors, including the type of test being used. There are three types of HIV diagnostic tests: nucleic acid tests (NAT), antigen/antibody tests, and antibody tests.

  • A Nucleic acid test (NAT)

looks for the actual virus in the blood and involves drawing blood from a vein. The test can either tell if a person has HIV or tell how much virus is present in the blood (known as an HIV viral load test). While a NAT can detect HIV sooner than other types of tests, this test is very expensive and not routinely used for screening individuals unless they recently had a high-risk exposure or a possible exposure and have early symptoms of HIV infection.

When to get tested for HIV
  • Antibody/antigen combination tests

look for both HIV antibodies and antigens. Antibodies are produced by your immune system when you’re exposed to viruses like HIV. Antigens are foreign substances that cause your immune system to activate. If you have HIV, an antigen called p24 is produced even before antibodies develop. Antigen/antibody tests are recommended for testing done in labs and are now common in the United States. An antigen/antibody test performed by a laboratory on blood from a vein can usually detect HIV infection 18 to 45 days after an exposure. There is also a rapid antigen/antibody test available that is done with a finger prick. Antigen/antibody tests done with blood from a finger prick can take longer to detect HIV (18 to 90 days after an exposure).

  • Antibody screening tests

look for antibodies to HIV in your blood or oral fluid. Antibody tests can take 23 to 90 days to detect HIV infection after an exposure. In general, antibody tests that use blood from a vein can detect HIV sooner after infection than tests done with blood from a finger prick or with oral fluid. Most rapid tests and the only currently approved HIV self-test are antibody tests.

An initial HIV test usually will either be an antigen/antibody test or an antibody test. If the initial HIV test is a rapid test or a self-test and it is positive, the individual should go to a health care provider to get follow-up testing. If the initial HIV test is a laboratory test and it is positive, the laboratory will usually conduct follow-up testing on the same blood sample as the initial test. Although HIV tests are generally very accurate, follow-up testing allows the health care provider to be sure the diagnosis is right.

Test Accuracy

HIV tests are highly accurate if used correctly. However, some testing methods are more reliable than others. Improper use or storage can also undermine the accuracy of a test.

Certain conditions can also trigger a false-positive test result, meaning that the test shows positive for HIV while the person is not actually HIV-positive. Conditions that can trigger a false positive include syphilis, lupus, and Lyme disease. Confirmatory testing will almost always weed out these incorrect findings.

Risks and Contraindications

There are no contraindications for HIV testing, meaning there is nothing that makes getting tested inadvisable. Also, there are few risks. If a blood draw is required, you may experience soreness, swelling, and bruising at the injection site. Light-headedness and testing HIV positive are also possible.

If you are afraid of needles or are squeamish about blood, let the nurse or phlebotomist (healthcare professional who draws blood) know in advance. Other testing options may be available. Additionally, if you have hemophilia (a blood disorder that interferes with blood clotting) or if you are taking blood thinners, a child-sized butterfly needle may be used to reduce the risk of bleeding.

Timing is an important part of HIV testing.

If you have been exposed to HIV, there will be a period of time, called the window period, when the test cannot deliver an accurate result.

Because HIV tests generally detect antibodies and/or antigens, you need to wait until your body has produced enough of these to get an accurate result. If you test too early, you will get a false-negative reading. Even with the nucleic acid test, you need to wait until the virus has replicated to detectable levels.

Because detectable levels can vary by individual, most clinics will advise you to wait to be tested for HIV after possible exposure, according to the following timetable:

  • One to three weeks before getting a NAT
  • One month before getting a combination HIV Ag/Ab test
  • Three months before getting any of the other HIV tests

The procedure itself involves three steps: pre-test counseling, the HIV test, and post-test counseling. Depending on the test being performed, the process can take 30–45 minutes. Walk-in centers may take far longer.

How long does it take to get results?

  • Laboratory tests (NATand antigen/antibody) require blood to be drawn from your vein into a tube and then that blood is sent to a laboratory for testing. The results may take several days to be available.
  • With a rapid antibody screening test, usually done with blood from a finger prick or with oral fluid, results are ready in 30 minutes or less.
  • The rapid antigen/antibody test is done with a finger prick and takes 30 minutes or less.
  • The oral fluid antibody self-test provides results within 20 minutes.

Rapid tests involve a 3 month window. This means the results tell you your HIV status three months ago. A positive result from a rapid test always needs to be confirmed by a different laboratory test. If you have had other recent risks, a negative result needs to be confirmed in three months.

How soon after an exposure to HIV can a test detect if I have the virus?

No HIV test can detect HIV immediately after infection. If you think you’ve been exposed to HIV in the last 72 hours, talk to your health care provider about post-exposure prophylaxis (PEP), right away.

The time between when a person may have been exposed to HIV and when a test can tell for sure whether they have the virus is called the window period. The window period varies from person to person and depends on the type of test used to detect HIV. Ask your health care provider or test counselor about the window period for the test you’re taking.

  • A nucleic acid test (NAT)can usually tell you if you have HIV infection 10 to 33 days after an exposure.
  • An antigen/antibody test performed by a laboratory on blood from a vein can usually detect HIV infection 18 to 45 days after an exposure. Antigen/ antibody tests done with blood from a finger prick can take longer to detect HIV (18 to 90 days after an exposure).
  • Antibody tests can take 23 to 90 days to detect HIV infection after an exposure. Most rapid tests and self-tests are antibody tests. In general, antibody tests that use blood from a vein can detect HIV sooner after infection than tests done with blood from a finger prick or with oral fluid.

If you get an HIV test after a potential HIV exposure and the result is negative, get tested again after the window period. Remember, you can only be sure you are HIV-negative if:

  • Your most recent test is after the window period.
  • You haven’t had a potential HIV exposure during the window period. If you do have a potential exposure, then you will need to be retested.

Who Should Get an HIV Test?

You should be tested more often — at least once a year — if you’re at higher risk of getting HIV, including if you:

  • Have had several sexual partners
  • Had unprotected sex with someone who is or could be HIV-positive, including someone whose sexual history you don’t know
  • Injected drugs with a needle, syringe, or other device that someone else used first
  • Have had or are getting tested for tuberculosis, hepatitis, or any sexually transmitted disease, including syphilis, gonorrhea, chlamydia, or herpes
  • Have had sex for drugs or money
  • Had sex with someone who has a history of any of these

When to get tested for HIV?

This HIV test is not reliable until 90 days after infection. You need to get tested at least 90 days after the date you may have been infected. You can get tested sooner, but your result may not be reliable and you need to re-test to confirm your result once the 90 days have passed.

HIV Test Results

Understanding a Negative Result

What does a negative test result mean?

  • A negative result doesn’t necessarily mean that you don’t have HIV. This is due to the window period.
  • If you test again after the window period, have no possible HIV exposure during the window period, and the result comes back negative, you do not have HIV.
  • If you’re sexually active or use needles to inject drugs, continue to take actions to prevent HIV, like taking medicines to prevent HIV if you’re at high risk.
  • If you have certain risk factors, you should continue getting tested at least once a year. Learn more about who is at risk for HIV and why they should be tested more often.

If I have a negative result, does that mean my partner is HIV-negative also?

  • No. Your HIV test result reveals only your HIV status.
  • HIV is not necessarily transmitted every time you have sex or share needles, syringes, or other drug injection equipment. And the risk of getting HIV varies depending on the type of exposure or behavior. It is important to remember that taking an HIV test is not a way to find out if your partner has HIV.
  • It’s important to be open with your partners and ask them to tell you their HIV status. But keep in mind that your partners may not know or may be wrong about their status, and some may not tell you if they have HIV even if they are aware of their status. Consider getting tested together so you can both know your HIV status and take steps to keep yourselves healthy.

Understanding a Positive Result

What does a positive result mean?

  • If you use any type of antibody test and have a positive result, you will need another (follow-up) test to confirm your results.
  • If you test in a community testing program or take a self-test and it’s positive, you should go to a health care provider to get follow-up testing.
  • If your test is done in a health care setting or a lab and it’s positive, the lab will conduct the follow-up testing, usually on the same blood sample as the first test.
  • If the follow-up test is also positive, it means you have HIV (or are HIV-positive).
  • It is important that you start medical care and begin HIV treatment as soon as you are diagnosed with HIV. Antiretroviral therapy or ART (taking medicine to treat HIV infection) is recommended for all people with HIV, regardless of how long they’ve had the virus or how healthy they are. HIV medicine works by lowering the amount of virus in your body to very low levels. HIV medicine can make the viral load so low that a test can’t detect it (called an undetectable viral load). HIV medicine slows the progression of HIV and helps protect your immune system. If you take HIV medicine as prescribed and get and keep an undetectable viral load, you can stay healthy for many years. Having an undetectable viral load also helps prevent transmitting the virus to others. For example, if you have an undetectable viral load, you have effectively no risk of transmitting HIV to an HIV-negative partner through sex.

If I test positive for HIV, does that mean I have AIDS?

No. Being HIV-positive does not mean you have AIDS. AIDS is the most advanced stage of HIV disease. HIV can lead to AIDS if a person does not get treatment or take care of their health. But if a person with HIV takes their HIV medicine as prescribed, they may stay healthy for many years, and may never be diagnosed with AIDS.

Where Can You Get Tested for HIV?

  • Your health care provider’s office
  • Health clinics or community health centers
  • STD or sexual health clinics
  • Your local health department
  • Family planning clinics
  • VA medical centers
  • Substance abuse prevention or treatment programs
  • Many pharmacies and some community-based organizations also offer HIV testing.
  • You can also buy a home testing kit at a pharmacy or online.

References

Types of HIV tests https://www.cdc.gov/hiv/basics/hiv-testing/test-types.html
HIV Testing https://www.webmd.com/hiv-aids/hiv-aids-screening
What Tests Can Diagnose HIV? https://www.verywellhealth.com/hiv-diagnosis-3132731
HIV Testing https://hivinfo.nih.gov/understanding-hiv/fact-sheets/hiv-testing
HIV Testing Locations https://www.hiv.gov/hiv-basics/hiv-testing/learn-about-hiv-testing/where-to-get-tested