HIV Testing

Human immunodeficiency virus (HIV) is a virus that can be transmitted through contact with certain infected body fluids. If left untreated, HIV can progressively destroy the body’s ability to fight serious infections and cancers.

HIV tests use blood, oral fluid, or urine samples to detect the presence of the HIV virus, HIV antigens, and/or HIV antibodies produced by the body in response to an HIV infection. HIV testing is the only way to know if a person has HIV.

The purpose of HIV tests are to determine the presence of an HIV infection using blood, oral fluid, or urine samples. HIV tests may be used as a routine screening test, as a diagnostic test after possible exposure to HIV, or in patients with symptoms of an HIV infection.

What does the test measure? 

HIV tests detect the presence of the HIV virus, HIV antigens, and/or HIV antibodies. If these substances are detected, the test returns a positive result for HIV. 

There are three types of HIV tests available:

• Antibody test: Antibodies are produced by the body after an HIV infection. It can take weeks for the body to produce antibodies, so HIV antibody tests can only detect HIV from 3 to 12 weeks after infection.
• Antigen/antibody test: Antigens are foreign substances that activate an immune response. Antigens appear before the body produces antibodies, so HIV antigen/antibody tests can detect an HIV infection earlier than antibody tests, within 2 to 4 weeks of becoming infected. 
• HIV viral load test: An HIV viral load test looks for the quantity of HIV virus in the blood. In addition to detecting an HIV infection, viral load testing can also detect how much of the virus is in the blood. Although this type of testing can detect an HIV infection earlier than other HIV tests, it’s very expensive and is typically only used when someone has symptoms or a possible exposure to HIV.

HIV testing involves an initial test and, if the preliminary result is positive, additional follow-up testing to confirm these results. Laboratory testing uses blood samples to look for evidence of HIV. Rapid testing provides faster results from oral fluid, a fingerstick, or urine and can be administered on-site in a variety of health care and community settings.

Before the test

For an HIV test administered in a medical facility or lab, there is no preparation needed before the test. The type of HIV test administered depends on a person’s reason for getting tested, so it’s important to talk to a health care professional if you believe you’ve been exposed to HIV or have experienced symptoms of an HIV infection.

At-home HIV test kits offer detailed instructions for collecting a sample and administering the HIV test. Although test kits are designed to make the process straightforward, it’s important to read all instructions to reduce errors and contamination.

During the test

When an HIV test is administered in a medical facility or lab, a health care professional will instruct you on how the blood, oral fluid, or urine sample will be taken.

Laboratory-based HIV tests will take a blood sample through a vein in your arm. This process takes less than 5 minutes and some people feel moderate discomfort, such as pain or stinging where the needle is inserted into the arm. There is no discomfort when the sample is taken from an oral swab or urine.

At-home HIV tests use a sample of oral fluid to check for HIV. During this test, a device is used to swab the gums then inserted into a vial of testing solution. After 20-40 minutes, results can be read.

After the Test

If blood was drawn from a vein, pressure is placed on the puncture site with a clean gauze or cotton ball. You may be instructed to keep the gauze in place to reduce bruising. Although there are slight risks from a blood draw, including infection and lightheadedness, there are no restrictions on activity after the blood draw is complete.

Rapid HIV tests that use blood from a fingerstick, oral fluid or urine require no precautions or post-test restrictions. Some at-home HIV tests require samples to be mailed to a certified laboratory according to the instructions contained in the test kit.

Receiving test results

How long it takes to get results from an HIV test depends on the type of test administered:

• Laboratory tests: Both viral load and antigen/antibody tests that are performed in a laboratory require blood to be sent out for testing. The results of these tests often take several days before being available.
• Rapid antibody tests: Rapid antibody tests are performed on oral fluid or blood from a fingerstick. Results for these tests are ready in 30 minutes or less.
• Rapid antigen/antibody tests: Rapid antigen/antibody tests use blood from a fingerstick and take 30 minutes or less to produce results.
• At-home oral fluid antibody tests: At-home HIV testing uses a sample of oral fluid and provides results within about 20 to 40 minutes.

For HIV tests conducted at a medical facility or community organization, a trained staff member will report your results and be available to answer any questions. Health care providers can also discuss your risk factors for HIV and advise you on next steps if the results of the HIV test are positive. 

After rapid testing, you wait for the results in the facility. For laboratory testing that takes several days to receive results, you may be asked to schedule a follow-up visit or consent to receiving results by telephone.

For at-home HIV testing, results can be read according to instructions contained in the test kit. Test kits may also contain an information booklet designed to instruct users on what to do once they have obtained their test results.

Interpreting test results

HIV test results are reported as positive, negative, or indeterminate. The results of HIV tests should be interpreted with caution, as follow-up testing is often necessary and patients must take into account the test’s window period.

A window period is the time between when a person gets infected with HIV and when a test can detect the infection. No test can detect HIV immediately after infection and all HIV tests have a window period. The length of the window period varies from test to test, ranging from about 2 to 12 weeks. At-home tests have a window period of about 3 months. 

A negative HIV test result means that HIV antibodies or antigens weren’t detected in the test sample. If a person has had no potential exposure to HIV within the test’s window period, they are considered negative for HIV infection. If a person has had potential exposure within the test’s window period, HIV testing must be repeated after they are past the window period.

Positive results on an HIV test need to be confirmed through follow-up testing. Laboratory tests conduct the second test on the same blood sample as the first test. If a person receives a positive result on a rapid test, the health care professional will schedule a second confirmatory test. Positive results on an at-home HIV test must be confirmed in a laboratory or health care setting. If the follow-up HIV test result is also positive, a person is considered HIV-positive.

Indeterminate results on an HIV test occur when an initial screening test is positive, then a follow-up test is negative. In this situation, doctors may order the more detailed HIV viral load test for additional confirmation.

Other related tests

• CD4 Count
• HIV Viral Load
• HIV Drug Resistance Testing, Genotype

These resources provide detailed information about HIV, including symptoms, transmission, and treatment: 

• HIV.gov
• National Library of Medicine: HIV/AIDS
• CDC: HIV
• National Institute of Allergy and Infectious Diseases: HIV/AIDS

Sources

A.D.A.M. Medical Encyclopedia. Screening and diagnosis for HIV. Updated February 26, 2021. Accessed March 31, 2021. https://medlineplus.gov/ency/article/003538.htm

Centers for Disease Control and Prevention. Find an HIV test. Updated October 20, 2020. Accessed March 31, 2021. https://www.cdc.gov/hiv/basics/hiv-testing/finding-tests.html

Centers for Disease Control and Prevention. What are HIV and AIDS?. Updated March 29, 2021. Accessed March 31, 2021. https://www.cdc.gov/hiv/basics/hiv-testing/test-types.html 

Centers for Disease Control and Prevention. HIV/AIDS preventive services coverage. Updated May 5, 2020. Accessed March 31, 2021. https://www.cdc.gov/nchhstp/highqualitycare/preventiveservices/hivaids.html

Centers for Disease Control and Prevention. Information regarding the OraQuick In-Home HIV Test. Updated June 3, 2020. Accessed March 31, 2021. https://www.fda.gov/vaccines-blood-biologics/approved-blood-products/information-regarding-oraquick-home-hiv-test

MedlinePlus: National Library of Medicine. HIV screening test. Updated March 3, 2021. Accessed March 31, 2021. https://medlineplus.gov/lab-tests/hiv-screening-test/ 

Sax PE. Screening and diagnostic testing for HIV infection. In: Hirsch MS, ed. UpToDate. Updated September 9, 2020. Accessed March 31, 2021. https://www.uptodate.com/contents/screening-and-diagnostic-testing-for-hiv-infection 

U.S. Department of Health & Human Services. What are HIV and AIDS?. Updated June 5, 2020. Accessed March 31, 2021. https://www.hiv.gov/hiv-basics/overview/about-hiv-and-aids/what-are-hiv-and-aids