These tests used to be the gold standard in HIV testing. HIV tests have since changed and evolved, making them a less preferred method of checking for HIV.
Now, most laboratories use an immunoassay for the HIVp24 antigen and antibodies to HIV-1 and 2, followed by a confirmatory immunoassay to distinguish between HIV-1 and HIV-2.
Explaining the tests
The ELISA test is a blood antibody test that checks for proteins the body makes if HIV is present.
The Western blot and ELISA tests are two of the blood tests that can detect the HIV antibody. Laboratory blood tests can diagnose HIV through detecting certain antibodies or proteins produced by the immune system in response to the virus.
While the ELISA test is recommended in the course of testing, the Western blot test is no longer considered reliable.
The ELISA test, also called the EIA for enzyme immunoassay, checks for certain proteins that the body makes in response to HIV. The blood sample will be added to a petri dish that contains the virus.
If the blood contains antibodies to HIV, it will bind with the antigen and cause the dish's contents to change color. This very sensitive test was the first one widely used to check for HIV.
The Western blot test used to confirm the findings of the ELISA test by also detecting HIV antibodies. However, this test is not widely used anymore in the course of HIV testing.
The Western blot test is a more complicated blood test to perform, though the mechanics of the blood draw are the same. In this test, the sample is separated with an electrical current and transferred onto a piece of blotting paper. Here, an enzyme is added to cause color changes that signal the presence of HIV antibodies.
What are they used for?
The ELISA test is one of the first blood tests used to check for a number of diseases, including HIV. It can be used to see whether HIV antibodies are present in the blood or not.
The Western blot test was previously used to confirm the findings of the ELISA test. As newer tests have been introduced, it is not used as often.
Who has them?
Screening of all adults has been recommended at least once in a person's life, as well as routinely in pregnant women.
The Western blot and ELISA tests are only recommended if there is a risk that a person has contracted or been exposed to HIV.
People with a high risk for contracting HIV include the following individuals:
- people who have unprotected sex, especially with someone who has HIV
- IV drug users
- people who had blood transfusions or injections prior to 1985
- those with other sexually transmitted diseases (STDs)
Some people choose to get tested for HIV fairly regularly even if they are not at higher risk for the infection, especially if they have had a new sexual partner or work in healthcare situations.
Both the western blot and ELISA tests are conducted by taking a blood sample.
There is no special preparation for the ELISA or Western blot tests. Both tests are simple blood tests.
Anyone undergoing HIV testing may want to tell the laboratory technician if they have a fear of needles or blood draws. Additionally, some people may find it helpful to seek support from a relative or friend during HIV testing.
Risks and considerations
There are very few physical risks to consider for either of these tests.
When using the ELISA test for HIV screening, it is important to be aware of the window of exposure. It is possible to take the ELISA test too soon after exposure for the body to produce enough antibodies to cause a positive result, even though the virus is present.
What to expect: Before, during, and after the tests
Both the Western blot test and the ELISA test are standard blood tests and the procedure is the same for each test.
Before the test, the person having the testing done may sign a consent form. The medical technician should explain the test and answer any questions.
Then, for either test, the medical professional will do the following:
- examine the arm to find a suitable vein to draw blood from
- clean the test site with an antiseptic solution to reduce the bacteria on the skin's surface
- apply a tourniquet to make the veins fill with blood
- insert a needle into the vein and remove the tourniquet so that the needle can fill
- remove the needle and apply a little pressure and a bandage to the puncture site
After the test, there is no need to rest. The patient can drive home and go about their day as normal.
A negative HIV result from a Western blot test may not guarantee that a person does not have HIV.
The results are not as cut and dry as positive or negative on either test. Because the ELISA test is extremely sensitive, some people may test falsely positive.
Other infections such as lupus, Lyme disease, and other STDs may cause a false positive for HIV on the ELISA test. Because of this, positive ELISA test results need to be confirmed through another test.
However, if both the ELISA test and the Western blot test show HIV, an HIV infection is present.
What happens next?
What happens next depends on the results of the tests.
Even if the results of both tests were negative, it is not safe to assume that the person does not have HIV if the potential exposure to the virus happened within 3 months of taking the test. In this case, a person should repeat testing in 3 months and take proper precautions to prevent spreading a potential infection.
If a negative result has occurred and the person has not had exposure to HIV, a doctor may not recommend further testing.
If either test is positive, it is crucial to consult with a doctor immediately. A doctor may recommend further testing for confirmation of an HIV infection.
The doctor will probably also prescribe antiretroviral medications and make recommendations to prevent the disease from being transmitted via intravenous use or sexual intercourse.
There are many types of HIV tests available. While the ELISA test may still be used in HIV screenings, the following tests could also be considered:
- Other antibody tests: Like the ELISA and Western blot tests, these tests check for the antibody in the blood, saliva, and urine.
- Antigen or antibody tests: These tests check for both the presence of the virus and the virus's antibodies, making them extremely accurate for early detection. These tests are only available using blood tests.
- NATs: This test is used to detect HIV between 7 and 28 days following a high-risk exposure. While this test is the most accurate for recent exposure, it is extremely expensive and only used in situations where exposure has occurred.