HIV Screening: Tests That Diagnose HIV

The only way to know if you have HIV is to get an HIV test.

Several types of tests check your blood or body fluids to see if you're infected. Most can't detect HIV right away, because it takes time for your body to make antibodies or for enough virus to grow inside you. It may be up to 6 months before you'll see a positive result, which means an early test could be negative even though you're infected.

If you do have the virus, finding out quickly means you can start treatment to help you live a long and full life. You can also take precautions so that you don't pass HIV to other people.

Antibody Screening Tests

These tests check for a kind of protein that your body makes in response to the HIV infection, 2-8 weeks later. They're also called immunoassay or ELISA tests. They're generally very accurate, but they won't catch early infections.

Usually, a technician will take a small blood sample and send it to a lab for testing. Some immunoassay tests check urine or fluids from your mouth (not saliva), but there aren't as many antibodies in these, so you may not get a positive result even if you're infected. (That's called a false negative.)

Rapid versions of these blood and oral fluid tests can give results in under 30 minutes, but they may give false negatives, too.

Antibody/Antigen Combination Tests

The CDC recommends these blood tests. They can detect HIV as soon as 20 days earlier than antibody screening tests. They check for HIV antigen, a protein called p24 that's part of the virus that shows up 2-4 weeks after infection, as well as HIV antibodies.

A rapid antibody/antigen test can give you results in 20 minutes.

RNA Test

This looks for the virus itself and can diagnose HIV about 10 days after you've been exposed. It's expensive, though, so it's usually not the first test. But if you're at high risk and you have flu-like symptoms, your doctor may want to use it.

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In-Home Test Kits

Two kits are available in the U.S. You can buy them at your local store or online. Make sure the one you choose is FDA-approved.

One option is to prick your finger to get a small blood sample that you send to a lab. You call to get your result within a few business days, and it's anonymous (you don't have to give your name). If it's positive, the lab will also do a follow-up test.

For the other, you'll swab your upper and lower gums and test the sample in a vial. You get a result in 20 minutes. Maybe 1 in 12 people get a false negative from this test. You should get a lab test of your blood if it's positive.

To get a positive result from a home blood test, you'll have to be infected with HIV longer than you would with the in-person tests above. The home oral fluid test needs even more time.

Results and Follow-up Tests

A positive result means there were traces of HIV. If you had a rapid test, you should get a standard lab test to confirm it. If you had a lab test, more detailed tests on your blood sample can help confirm the diagnosis:

  • Antibody differentiation, between HIV-1 and HIV-2
  • Western blot or indirect immunofluorescence assay
  • HIV-1 nucleic acid test, which looks for the virus itself
  • RNA test

If you got an HIV test within the first 3 months after you could have been infected and it was negative, get another test at 6 months to be sure.

When Should You Get Tested?

You could have an HIV infection 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 equipment someone else had used first
  • Have had or are getting tested for TB or any sexually transmitted disease, including herpes and hepatitis
  • Have had sex for drugs or money
  • Had sex with someone who has a history of any of these

Pregnant women should also get tested.

Your doctor's office can do an HIV test. To find out where else you can get tested, check www.aids.gov or gettested.cdc.gov, or call 800-CDC-INFO (800-232-4636). Clinics that do HIV tests keep your results secret; some may do tests anonymously.

WebMD Medical Reference Reviewed by Lisa Bernstein, MD on October 25, 2016

Sources

SOURCES:

CDC: "National HIV and STD Testing Resources: Frequently Asked Questions."

AVERT: "HIV Testing," "Continuing antiretroviral (ARV) treatment."

AIDS.gov: "HIV Test Types."

Home Access Health Corporation: "The Home Access HIV-1 Test System."

Patel, P. J Clin Virol, "Rapid HIV screening: Missed opportunities for HIV diagnosis and prevention," May 2012.

Aberg, J. Clinical Infectious Diseases, 2009.

FDA: "FDA Approves First Over-the-Counter Home Use HIV Test Kit," "FDA approves first rapid diagnostic test to detect both HIV-1 antigen and HIV-1/2 antibodies," "Complete List of Donor Screening Assays for Infectious Agents and HIV Diagnostic Assays."

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