Anti-HIV Test (ELISA)

Anti-HIV Test (ELISA)


To test for HIV, a series of blood screenings may be done, including one called the ELISA test.


What are the ELISA test and the HIV differentiation assay?


The enzyme-linked immunosorbent assay (ELISA), also known as an enzyme immunoassay (EIA), detects HIV antibodies and antigens in the blood. The ELISA test is typically the first test ordered by a healthcare provider. In case of a positive result from this test, the ELISA test was previously followed by a test called a Western blot to confirm the diagnosis. However, the Western blot is no longer used, and today the ELISA test is followed by an HIV differentiation assay to confirm HIV infection. The provider may also order an HIV genetic material detection test.


When is the ELISA test recommended?


The ELISA test is recommended if a person has been exposed to HIV or is at risk of contracting HIV. Those at risk for contracting HIV include:

  • people who use intravenous (IV) drugs

  • people who have sex without a condom, especially with someone who has HIV or an unknown HIV status

  • people who have had sexually transmitted diseases (STDs) 

People may opt to have the test done if they’re uncertain about their HIV status, even if they’re not in a high-risk group. For people who participate in high-risk behaviors, such as IV drug use or sex without a condom, it’s a good idea to get tested on a regular basis.


What happens during the test?


Before the test, a healthcare provider will explain the procedure. The person having the test will probably need to sign a consent form.

To help prevent any problems during the test, the person should be sure to tell the healthcare provider if:


During the test


The procedure for getting a sample of blood is the same for both tests. A medical professional will:

  • clean the skin site where they plan to draw blood

  • apply a tourniquet, or elastic band, around the arm to make the veins swell with blood

  • place a needle into one of the veins and draw a small sample of blood into a tube

  • remove the needle and apply a bandage

To decrease further bleeding, after the test the person may be asked to elevate or flex their arm to reduce blood flow. Giving a blood sample isn’t painful, though the person may feel a sting or a pricking sensation as the needle goes into their vein. Their arm may throb slightly after the procedure.


Testing the blood


For the ELISA test, the blood sample will be sent to a laboratory for analysis. A lab technician will add the sample to a device that contains HIV antigens and anti-HIV antibodies. An automated process will add an enzyme to the device. The enzyme helps speed up chemical reactions. Afterward, the reaction of the blood and the antigen will be monitored. If the blood contains antibodies to HIV or antigens of HIV, it will bind with the antigen or antibody in the device. If this binding is detected, the person may have HIV.

The differentiation assay is very similar, but instead of an automated machine, the device can be handled by a lab technician. The specific antibodies and antigens in the blood are separated and identified in a different immunoassay device.