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ELISA/Western Blot Tests for HIV

About HIV

Human immunodeficiency virus (HIV) is a virus that attacks the immune system. If it is not treated, it can develop into acquired immunodeficiency syndrome (AIDS), which is a prolonged and fatal illness. HIV is spread through vaginal, oral, or anal sexual contact. It is 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 have been exposed to HIV or are at risk for contracting HIV. Those at risk for HIV include:

  • intravenous (IV) drug users
  • people who have unprotected sex, especially with someone who has HIV or has 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 are uncertain about your HIV status, even if you are not in a high-risk group. It is a good idea to be 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 do not 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 or 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 so that 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 will 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 your inner arm 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 is not 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 (a protein that helps speed up chemical reactions) to the petri dish and watching 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 paper (blotting) 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:

  • feel lightheaded or faint, especially if you have a fear of needles or blood
  • get an infection at the site of the needle insertion
  • develop a bruise at the puncture site
  • have trouble stopping the bleeding

Make sure to tell your healthcare provider if you’ve had trouble giving blood in the past, bruise easily, or suffer from a bleeding disorder, such as hemophilia or are taking anticoagulant medications (also referred to as “blood thinners”). 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. Further testing is required 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 does not show up on the ELISA test even though you are infected. This can happen if someone is in the early stages of the infection, and his or her body has not 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.”

According to the Centers for Disease Control and Prevention (CDC), a person’s window period is usually between two and eight weeks, and the average is 25 days. 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 will 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 be emotionally devastating. Your healthcare provider can refer you to counseling or HIV support groups.

Although HIV is very serious, there is medication that can help prevent HIV infection from developing into AIDS, so that you can 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.

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