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HIV testing; HIV screening; HIV screening test; HIV confirmatory test
An HIV test shows whether you are infected with HIV (human immunodeficiency virus). HIV is a virus that attacks and destroys cells in the immune system. These cells protect your body against disease-causing germs, such as bacteria and viruses. If you lose too many immune cells, your body will have trouble fighting off infections and other diseases.
Types
There are three main types of HIV tests:
- Antibody Test. This test looks for HIV antibodies in your blood or saliva. Your immune system makes antibodies when you are exposed to bacteria or viruses, like HIV. An HIV antibody test can determine if you have HIV from 3–12 weeks after infection. That’s because it can take a few weeks or longer for your immune system to make antibodies to HIV. You may be able to do an HIV antibody test in the privacy of your home. Ask your health care provider about at-home HIV test kits.
- HIV Antibody/Antigen Test. This test looks for HIV antibodies and antigens in the blood. An antigen is a part of a virus that triggers an immune response. If you’ve been exposed to HIV, antigens will show up in your blood before HIV antibodies are made. This test can usually find HIV within 2–6 weeks of infection. The HIV antibody/antigen test is one of the most common types of HIV tests.
- HIV Viral Load. This test measures the amount of the HIV virus in the blood. It can find HIV faster than antibody and antibody/antigen tests, but it is very expensive. It is mostly used for monitoring HIV infections.
Other names: HIV antibody/antigen tests, HIV-1 and HIV-2 antibody and antigen evaluation, HIV test, human immunodeficiency virus antibody test, type 1, HIV p24 antigen test
What is it used for?
An HIV test is used to find out if you have been infected with HIV. HIV is the virus that causes AIDS (acquired immunodeficiency syndrome). Most people with HIV don’t have AIDS. People with AIDS have an extremely low number of immune cells and are at risk for life-threatening illnesses, including dangerous infections, a severe type of pneumonia, and certain cancers, including Kaposi sarcoma.
If HIV is found early, you can get medicines to protect your immune system. HIV medicines may prevent you from getting AIDS.
Why do I need an HIV test?
The Centers for Disease Control and Prevention (CDC) recommends that everyone between the ages of 13 and 64 gets tested for HIV at least once as part of routine health care. You may also need an HIV test if you are at higher risk for infection. HIV is mainly spread through sexual contact and blood, so you may be at a higher risk for HIV if you:
- Are a man that has had sex with another man
- Have had sex with an HIV-infected partner
- Have had multiple sex partners
- Have injected drugs, such as heroin, or shared drug needles with someone else
HIV can spread from mother to child during birth and through breast milk, so if you are pregnant your doctor may order an HIV test. There are medicines you can take during pregnancy and delivery to greatly reduce your risk of spreading the disease to your baby.
In general, testing for the human immunodeficiency virus (HIV) is a 2-step process that involves a screening test and follow-up tests.
SCREENING TESTS
These are tests that check if you’ve been infected with HIV. The most common tests are described below.
An antibody test (also called immunoassay) checks for antibodies to the HIV virus. Your health care provider may order the test for you to have done at a lab. Or, you may have it done at a testing center or use a home kit. These tests can detect antibodies starting a few weeks after you’re infected with the virus. Antibody tests can be done using:
- Blood — This test is done by drawing blood from a vein, or by a finger prick. A blood test is the most accurate because blood has a higher level of antibodies than other body fluids.
- Oral fluid — This test checks for antibodies in the cells of the mouth. It is done by swabbing the gums and inside cheeks. This test is less accurate than the blood test.
- Urine — This test checks for antibodies in the urine. This test is also less accurate than the blood test.
An antigen test checks your blood for an HIV antigen, called p24. When you’re first infected with HIV, and before your body has a chance to make antibodies to the virus, your blood has a high level of p24. The p24 antigen test is accurate 11 days to 1 month after getting infected. This test is usually not used by itself to screen for HIV infection.
An antibody-antigen blood test checks for levels of both HIV antibodies and the p24 antigen. This test can detect the virus as early as 3 weeks after getting infected.
FOLLOW-UP TESTS
A follow-up test is also called a confirmatory test. It is usually done when the screening test is positive. Several kinds of tests may be used to:
- Detect the virus itself
- Detect antibodies more accurately than screening tests
- Tell the difference between the 2 types of virus, HIV-1, and HIV-2
How the Test is Performed
HIV testing can be done by:
- Drawing blood from a vein
- A finger-prick blood sample
- An oral fluid swab
- A urine sample
How to Prepare for the Test
No preparation is necessary.
What happens during an HIV test?
You will either get a blood test in a lab or do your own test at home.
For a blood test in a lab:
- A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
For a home test, you will need to get a sample of saliva from your mouth or a drop of blood from your fingertip.
- The test kit will provide instructions on how to get your sample, package it, and send it to a lab.
- For a saliva test, you will use a special spatula-like tool to take a swab from your mouth.
- For a fingertip antibody blood test, you will use a special tool to prick your finger and collect a sample of blood.
For more information on at-home testing, talk to your health care provider.
How the Test will Feel
When taking a blood sample, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
There is no discomfort with an oral swab test or the urine test.
Why the Test is Performed
Testing for HIV infection is done for many reasons, including:
- Persons who want to be tested
- Persons in high-risk groups (men who have sex with men, injection drug users and their sexual partners, and commercial sex workers)
- Persons with certain conditions and infections (such as Kaposi sarcoma or Pneumocystis jirovecii pneumonia)
- Pregnant women, to help prevent them from passing the virus to the baby
Normal Results
A negative test result is normal. People with early HIV infection may have a negative test result.
What Abnormal Results Mean
A positive result on a screening test does not confirm that the person has an HIV infection. More tests are needed to confirm HIV infection.
A negative test result does not rule out HIV infection. There is a period of time, called the window period, between HIV infection and the appearance of anti-HIV antibodies. During this period, antibodies and antigens may not be measured.
If a person might have acute or primary HIV infection and is in the window period, a negative screening test doesn’t rule out HIV infection. Follow-up tests for HIV are needed.
Risks
With the blood test, veins and arteries vary in size from one patient to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
There are no risks with the oral swab and urine tests.
