To screen for and diagnose human immunodeficiency virus (HIV) infections
HIV Tests
HIV Tests
Also Known As
HIV Antibody and HIV Antigen (p24)
HIV Screening Tests
AIDS Test
AIDS Screen
HIV Serology
p24 Antigen
Formal Name
HIV-1 and HIV-2 Antibody and Antigen Evaluation
This article was last reviewed
on
This article waslast modified
on August 31, 2020.
At a Glance
Why Get Tested?
When To Get Tested?
- At least once, when you are 13 to 64 years old
- When you think you may have been exposed to the virus
- Before becoming pregnant or when pregnant
- Once a year if you are at increased risk of being exposed to the virus
Sample Required?
A blood sample collected from a vein or by pricking the tip of a finger (fingerstick) or saliva (oral fluid), which may be collected by swabbing your gums.
Test Preparation Needed?
None
Accordion Title
Common Questions
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How is the test used?
HIV tests are used to screen for and diagnose HIV infections.
Screening
Different types of tests may be used for HIV screening:
- Blood test for HIV antibody and HIV antigen (p24)—this is the recommended screening test for HIV. The tests that use a blood sample drawn from a vein can detect HIV infections in most people approximately 2 to 6 weeks after infection, while fingerstick blood tests can detect HIV infections 2 to 12 weeks after infection. This combination test increases the likelihood that an infection is detected by testing for both HIV antigen and antibodies:
- HIV antigen (p24)—the level of p24 antigen and the amount of virus (viral load) increase significantly soon after initial infection. Testing for p24 allows for detection of early infections, before HIV antibody is produced.
- Antibodies to HIV-1 and HIV-2—HIV-1 is the most common type found in the United States, while HIV-2 has a higher prevalence in parts of Africa. A few weeks after exposure to the virus, antibodies to HIV are produced in response to the infection and remain detectable in the blood thereafter, making the antibody test useful for detecting infections weeks after exposure.
- HIV antibody testing—all HIV antibody tests used in the U.S. detect HIV-1 and some tests can also detect HIV-2. These tests are available as blood tests or saliva tests. HIV antibody tests can detect infections in most people 3 to 12 weeks after infection.
Diagnosis
If any one of the above screening tests is positive, then it must be followed by a second test to confirm the diagnosis. This second test is an antibody test that is different than the first test. If the second test does not agree with the first test, then a third test is performed that detects the genetic material (RNA) of the virus. An HIV RNA test will detect HIV in most people by 1-4 weeks of infection.
- Blood test for HIV antibody and HIV antigen (p24)—this is the recommended screening test for HIV. The tests that use a blood sample drawn from a vein can detect HIV infections in most people approximately 2 to 6 weeks after infection, while fingerstick blood tests can detect HIV infections 2 to 12 weeks after infection. This combination test increases the likelihood that an infection is detected by testing for both HIV antigen and antibodies:
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When is it ordered?
Several organizations recommend routine screening for HIV:
- The Centers for Disease Control (CDC) and the American College of Physicians recommend that anyone between the ages of 13 and 64 be screened for HIV at least once.
- The U.S. Preventive Services Task Force (USPSTF) recommends anyone age 15 to 65 get at least a one-time test.
- The CDC, USPSTF and American College of Obstetricians and Gynecologists (ACOG) recommend that all pregnant women be screened. Repeat testing in the third trimester may be done for women at high risk. Some women may opt to get tested when planning a pregnancy (see Pregnancy: Preconception).
- The American Academy of Pediatrics advises that all sexually active youth be screened, and that youths between 15 and 18 years old be offered HIV testing at least once, regardless of sexual history.
For additional details on screening recommendations, see the articles for Teens, Young Adults, Adults, and Adults 50 and Up.
Annual screening is advised for those who are at high risk for HIV and is recommended when you:
- Have unprotected sex with more than one partner since your last HIV test
- Are a man who has sex with another man
- The CDC says that your healthcare practitioners may consider more frequent screening for you, such as every 3 to 6 months.
- Use street drugs by injection, especially when sharing needles and/or other equipment
- Exchange sex for drugs or money
- Have an HIV-positive sex partner
- Have sex with anyone who falls into one of the categories listed above or if you are uncertain about your sexual partner's risk behaviors
You should get at least a one-time test, regardless of age, if you:
- Are diagnosed with hepatitis B or hepatitis C, tuberculosis (TB) or a sexually transmitted disease (STD)
- Received a blood transfusion prior to 1985, or had a sexual partner who received a transfusion and later tested positive for HIV
- Are a healthcare worker with direct exposure to blood on the job (e.g., needlestick injury)
- Think you may have been exposed
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What does the test result mean?
- A negative HIV test usually indicates that you do not have an HIV infection. However, if you are screened too soon, the result may be negative despite the fact that you are infected (false negative). If an HIV test is negative but recent exposure is suspected, then an HIV RNA test or repeat testing with the HIV antigen/antibody blood test may be required.
Also, a negative screening test means only that there is no evidence of disease at the time of the test. If you are at increased risk of HIV infection, it is important to have screening tests performed on a yearly basis to check for possible exposure to the virus.
- If you test positive on both the initial screen and supplemental testing, then you are diagnosed with HIV.
The CDC recommends the following testing protocol to screen for and diagnose HIV infection:
- Screen for HIV infection using a combination HIV antigen/antibody test, then
- Verify a positive with a second HIV antibody test that differentiates between HIV-1 and HIV-2.
- If results of the first and second test do not agree, then the next test to perform is an HIV-1 RNA test (nucleic acid amplification test, NAAT). If the HIV-1 RNA is positive, then the test is considered positive.
- A negative HIV test usually indicates that you do not have an HIV infection. However, if you are screened too soon, the result may be negative despite the fact that you are infected (false negative). If an HIV test is negative but recent exposure is suspected, then an HIV RNA test or repeat testing with the HIV antigen/antibody blood test may be required.
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How can I get tested for HIV?
There are a few different ways you can get access to HIV screening:
- A blood or saliva sample can be collected in a healthcare practitioner's office or a local clinic and sent to a laboratory for testing. Certain testing centers provide either anonymous (the name is never given) or confidential (the name is given but kept private) HIV testing and counseling. You can also contact your state or local health department to find out where testing may be available. To find a testing site near you, visit the National HIV and STD Testing Resources webpage.
- In these same settings, there may be a rapid test available, with results that are generated in 20 minutes or less.
- There is a home test for HIV that has been approved by the U.S. Food and Drug Administration (FDA). It uses a saliva (oral fluid) sample and results are available in about 20 minutes.
The home test has two limitations:
1. The saliva test is less sensitive than a blood test, so the home test may miss some cases of HIV that a blood test would detect.
2. The home test is not as accurate when it is performed at home by a lay person compared to when it is performed by a trained healthcare professional. However, the convenience of home testing might encourage some people who might otherwise be reluctant to go to a healthcare practitioner or clinic to learn their HIV status.
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How soon can HIV be detected by a blood test?
It depends on the test. Combination tests that use a blood sample drawn from a vein and detect HIV antigen (p24) and HIV antibodies can detect HIV infections in most people 2 to 6 weeks after infection. Combination tests that use fingerstick blood samples detect HIV infections about 2 to 12 weeks after infection. Blood tests that detect HIV antibody alone can detect infections in most people about 3 to 12 weeks after infection.
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Should I tell anyone else of my test results?
Yes. If you test positive for HIV infection, it is important that you tell your healthcare practitioners as well as all current and future sex partners and/or anyone with whom you share needles. Counseling services are often available from the clinic that performed the test or from your healthcare provider that will help you to inform the people who need to know.
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How confidential are HIV test results?
Your HIV status, like other medical conditions and test results, is protected by the HIPAA Privacy Rule and cannot be shared with friends, family, or employers without your written permission. Your HIV status may be shared with your healthcare providers who have a "need to know" in order to treat you. Also, in order to determine the incidence of HIV and to provide appropriate prevention and care services, all new cases of HIV are reported to state and local health departments.
Certain testing centers provide either anonymous (your name is never given) or confidential (your name is given but kept private) HIV testing and counseling. You can also contact your state or local health department to find out where testing may be available.
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If I test positive for HIV, what follow-up tests are performed?
If you are HIV-positive, follow-up tests may include the following:
- HIV viral load testing—measures the amount of HIV in the blood. It is performed when you are first diagnosed to help determine the status of the disease and is ordered at intervals to monitor the effectiveness of therapy.
- CD4 count—measures the number of CD4 T-cells (lymphocytes) in the blood. It is ordered when you are first diagnosed to get a baseline assessment of your immune system and it is done at intervals to monitor therapy and the status of the immune system.
- HIV antiretroviral drug resistance testing, genotypic—ordered when you are initially diagnosed to determine whether the particular strain(s) of HIV that you have is resistant to certain antiretroviral drug therapies. This testing is also ordered when treatment is changed or when there is evidence of treatment failure.
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Can HIV be prevented?
There is currently no vaccine to protect you against HIV, but avoiding high-risk activities such as having unprotected sex and sharing needles for injecting drugs can help to prevent its spread.
While there is no vaccine, the CDC and the World Health Organization recommend that individuals without HIV infection but at high risk for it consider taking pre-exposure prophylaxis (PrEP), a daily pill to help prevent infection. For people taking PrEP consistently, the risk of HIV infection was significantly lower (up to 92%) compared to those who didn't take it.
If you have HIV, early diagnosis of your infection is important to prevent its transmission to others and to allow evaluation, monitoring, and treatment. Healthcare workers can protect themselves from HIV infection by following universal precautions, such as wearing gloves and avoiding needle sticks.
Post-exposure prophylaxis (PEP) is another strategy for preventing HIV. PEP is taking antiretroviral medication after recent possible exposure to the virus. PEP should only be used in emergency situations and must be taken within 72 hours of possible HIV exposure. Talk to your healthcare practitioner or emergency department doctor about PEP right away if you:
- Think you have may been exposed through sex (e.g., broken condom)
- Think you were exposed through sharing needles or other works for injecting drugs
- Were sexually assaulted
- Are a healthcare worker and think you were exposed to HIV at work
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Why should I get tested if I am pregnant?
If you are pregnant, it is important to determine if you have HIV so you can be treated. Treatment of HIV-infected mothers during pregnancy, precautions at birth, and avoiding breast-feeding can minimize the risk of passing the infection from mother to child. If you are already taking HIV medications when you become pregnant, you should continue to do so during pregnancy and labor and delivery. If you are not taking HIV medications or have a high viral load during pregnancy, giving the antiretroviral drug zidovudine intravenously during labor and delivery and also to the newborn twice a day by mouth for 6 weeks reduces the rate of transmission from 25-33% to about 1-2%.
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Can you use the HIV antibody test to detect HIV in newborns?
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What are the symptoms of HIV infection?
Symptoms of the initial HIV infection can mimic those of influenza and other viral infections. The only reliable way to tell if you are infected is to get tested. Many people with HIV do not experience symptoms for years after the initial infection or have symptoms that are very similar to symptoms of other illnesses. For more, see this CDC web page: About HIV.
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What are the treatments for HIV/AIDS?
Currently, there is no cure for HIV infection or AIDS. However, early diagnosis allows for treatment with antiretroviral therapy (ART) that can help to suppress levels of virus in your body (viral load) and greatly improve your long-term health. The U.S. Department of Health and Human Services (DHHS) as well as the World Health Organization recommend that all individuals diagnosed with HIV infection receive treatment as soon as possible, including pregnant women. With advances in treatment, individuals with HIV infection are living longer, healthier lives.
People typically take at least three drugs from two different classes in order to prevent or minimize virus replication and the emergence of drug-resistant strains. Combinations of three or more antiretroviral drugs are referred to as highly active antiretroviral therapy or HAART. Read the Treatment section of the article on HIV Infection and AIDS for additional details.