A human immunodeficiency virus (HIV) test detects HIV antibodies or antigens, or the genetic material (DNA or RNA) of HIV in the blood or another type of sample. This can show if an HIV infection is present (HIV-positive). HIV infects white blood cells called CD4+ cells. They are part of the body's immune system that help fight infections. HIV can progress to acquired immunodeficiency syndrome (AIDS).
After the original infection, it takes about 4 to 12 weeks for HIV antibodies or antigens to appear in the blood. The period between becoming infected with HIV and the point at which antibodies or antigens to HIV can be detected in the blood is called the seroconversion or "window" period. During this period, an HIV-infected person can still spread the disease, even though a test will not detect any antibodies or antigens in his or her blood.
Several tests can find antibodies to or genetic material (RNA) of the HIV virus. These tests include:
- Enzyme-linked immunosorbent assay (ELISA).
This test is usually the first one used to detect infection with HIV. If antibodies to HIV are present (positive), the test is usually repeated to confirm the diagnosis. If ELISA is negative, other tests usually aren't needed. This test has a low chance of having a false result after the first few weeks that a person is infected.
- Polymerase chain reaction (PCR).
This test finds either the RNA of the HIV virus or the HIV DNA in white blood cells infected with the virus. PCR testing isn't done as often as antibody testing, because it requires technical skill and expensive equipment. This test may be done in the days or weeks after exposure to the virus. Genetic material may be found even if other tests are negative for the virus. The PCR test is very useful to find a very recent infection, find out if an HIV infection is present when antibody test results were uncertain, and screen blood or organs for HIV before donation.
- Indirect fluorescent antibody (IFA).
This test detects HIV antibodies using a special fluorescent dye and a microscope. This test may be used to confirm the results of an ELISA test.
If HIV antibodies or antigens aren't found, the test may be repeated in a few months.
If you have a positive test result, contact your sex partners to inform them. They may want to be tested. You may be able to get help from your local health department to do this.
Home test kits
Some home test kits for HIV have been approved by the U.S. Food and Drug Administration (FDA). If the results from a home test kit show that you have an HIV infection, talk to a doctor. And keep in mind that these test kits sometimes may show that you have HIV when you don't (false-positive result). Or they may show that you don't have HIV when you do (false-negative result).
- A rapid home test kit gives you the results in an hour. For this test, you rub your gums with a swab supplied by the kit. Then you place the swab into a vial of liquid. The test strip on the swab shows if you have HIV or not.
- Another type of test kit for HIV is a home blood test kit. This kit provides instructions and materials for collecting a small blood sample by sticking your finger with a lancet. The blood is placed onto a special card that is then sent to a lab for analysis. You can find out your results over the phone by using an anonymous code number. Counseling is also available over the phone for people who use the test kit.
Why It Is Done
A test for the human immunodeficiency virus (HIV) is done to:
- Detect an HIV infection.
- Screen blood, blood products, and organ donors to prevent the spread of HIV.
- Screen pregnant women for HIV infection. Pregnant women who are infected with HIV and receive treatment are less likely to pass the infection on to their babies than are women who don't receive treatment.
- Find out if a baby born to an HIV-positive woman also is infected with HIV. A PCR test is often done in this case because the baby may get antibodies against HIV from the mother and yet not be infected.
This test is not done to find out if a person has AIDS. A diagnosis of AIDS means that a person is HIV-positive and other problems are present.
How To Prepare
In general, there's nothing you have to do before this test, unless your doctor tells you to.
A test for HIV infection can't be done without your consent. Most doctors offer counseling before and after the test to discuss:
- How the test is done, what the results mean, and any other tests that may be done.
- How the diagnosis of an HIV infection may affect your social, emotional, professional, and financial outlooks.
- The benefits of early diagnosis and treatment.
Before the test, it's important to tell your doctor how and where to contact you when your test results are ready. If your doctor has not contacted you within 1 to 2 weeks of your test, call and ask for your results.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm.
How It Feels
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Your doctor may ask you to come back to talk about your results. This may happen no matter what your results say. It does not always mean that you have HIV.
- A normal result means that no HIV antibodies or antigens were found in your blood. Normal results are called negative.
- You may need a repeat test to be sure the results are correct. If a repeat test at 3 months is negative, there is no infection.
- If the results aren't clear, it's called an indeterminate result. This may happen before HIV antibodies or antigens develop. Or it may happen when some other type of antibody or antigen interferes with the results. If this occurs, you will probably have another test right away.
- An abnormal result means that you have HIV antibodies or antigens in your blood. These results are called positive.
- A positive test is repeated on the same blood sample. If two or more results are positive, they must be confirmed by another type of test. This is because some tests can cause false-positive results. No one is considered HIV-positive until the result is confirmed by a test that shows HIV RNA in the person's blood.
- If your test result is positive, you will get counseling. You can learn how to handle the results and what to do next.
- If you have a positive test result, contact your sex partners to tell them. They should be tested. You may be able to get help from your local health department in contacting your sex partners. In many places, a health department employee will contact you to offer this help.
Current as of: February 9, 2022
Author: Healthwise Staff
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Peter Shalit MD, PhD - Internal Medicine