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ELISA/Western Blot Tests For HIV

About HIV

HIV is a virus that attacks the immune system. If it isn’t treated, it can develop into AIDS, which is a prolonged and often fatal illness. HIV is spread through vaginal, oral, or anal sexual contact. It’s also spread through blood, blood factor products, injection drug use, and breast milk.

What is the ELISA/Western blot test?

A series of blood screenings are performed to test for HIV. The enzyme-linked immunosorbent assay (ELISA), also known as an enzyme immunoassay (EIA), is the first test that your healthcare provider will order to screen for HIV. ELISA, like the Western blot test, detects HIV antibodies in your blood. Antibodies are proteins your immune system produces in response to the presence of foreign substances, such as viruses. If you test positive for HIV on the ELISA test, your provider will order the Western blot test to confirm HIV infection.

When is this test recommended?

The ELISA and Western blot tests are recommended if you’ve been exposed to HIV or are at risk for contracting HIV. Those at risk for HIV include:

  • people who use intravenous (IV) drugs
  • people who have unprotected sex, especially with someone who has HIV or an unknown HIV status
  • people who have had sexually transmitted diseases (STDs)
  • people who had blood transfusions or blood clotting factor injections before 1985

You may opt to have the test done if you’re uncertain about your HIV status, even if you’re not in a high-risk group. It’s a good idea to get tested on a regular basis if you participate in high-risk behaviors, such as IV drug use or unprotected sex.

How do I prepare for the test?

You don’t need to do anything to prepare for the ELISA or Western blot test. It takes very little time to give a blood sample, but it may take several days, and in some cases weeks, to get the results. Make sure to tell your healthcare provider as well as the laboratory technician if you have a fear of needles or faint at the sight of blood. They can take appropriate precautions to provide for your safety in the event that you should faint.

What happens during the test?

Before having these tests, you’ll probably need to sign a consent form. The test and procedure should be explained to you. The procedure for getting a sample of your blood is the same for both tests. A medical professional will:

  • clean the skin site where they plan to draw your blood with a solution to decrease the number of bacteria or germs on the skin surface overlying the vein that they intend to access for the blood sample
  • apply a tourniquet, or elastic band, around your arm to make the veins swell with blood
  • place a needle into one of your veins and draw a small sample of blood into a tube
  • remove the needle and apply a bandage

You may be asked to elevate or flex your arm to reduce the blood flow after the test, to decrease further bleeding.

Giving a blood sample isn’t painful, though you may feel a sting or a pricking sensation as the needle goes into your vein. Your arm may throb slightly after the procedure.

The blood sample will be sent to a laboratory for analysis. For the ELISA test, a lab technician adds the sample to a Petri dish containing HIV antigen. An antigen is any foreign substance, such as a virus, that causes your immune system to respond.

If your blood contains antibodies to HIV, it will bind with the antigen. The technician will check this by adding an enzyme, which helps speed up chemical reactions, to the petri dish. Afterward, they’ll watch how your blood and the antigen react. If the contents of the dish change color, you may have HIV.

The general process of a Western blot test is similar. However, the Western blot method is more complicated. It involves separating the HIV sample into its component proteins using an electrical current. Then, these proteins are transferred to a special kind of blotting paper and reacted with your blood sample. An enzyme is used to cause color change and detect antibodies.

Are there any risks?

These tests are very safe, but rare complications can occur. For example, you may:

Make sure to tell your healthcare provider if:

Contact your healthcare provider right away if you experience any of these complications.

What do the test results mean?

If you test positive for HIV on the ELISA test, you might have HIV. However, sometimes there can be false positives with the ELISA screen. This means that test results indicate that you have HIV when you actually do not. This is why more sophisticated tests such as the Western blot assay are performed to confirm whether you have the virus. For example, having certain conditions such as Lyme disease, syphilis, or lupus may produce a false positive for HIV in an ELISA test.

If you test positive on the ELISA screen, your healthcare provider will order a Western blot test. If you test positive for HIV with the Western blot test, you probably have HIV.

Sometimes, HIV doesn’t show up on the ELISA test even though you’re infected. This can happen if someone is in the early stages of the infection, and their body hasn’t produced enough antibodies (in response to the virus) for the tests to detect. This early stage of HIV infection, in which a person has HIV but tests negative for it, is known as the "window period." Learn more about HIV and its window period.

According to the Centers for Disease Control and Prevention (CDC), a person’s window period is usually between three and 12 weeks. However, in rare cases, some people can take as long as six months to develop antibodies.

After the test

Though both tests are simple and straightforward, waiting for the results can create anxiety. In many cases, you’ll have to talk to someone either in person or over the phone to receive your results, regardless of whether they are positive or negative. A positive test result can trigger strong emotions. Your healthcare provider can refer you to counseling or HIV support groups.

Although HIV is very serious, there’s medication that can help prevent HIV infection from developing into AIDS. It’s possible for you to live a full and long life. The earlier you discover your HIV status, the earlier you can begin treatment to prevent health complications or transmission of the infection to others.

Content licensed from:

Written by: Tricia Kinmanon: Jul 06, 2017

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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