What are the Western blot and ELISA tests for HIV?
In the past, the Western blot test was used to confirm the results of an ELISA test.
However, advances in technology mean that other methods are now commonly used. Since 2014, the Centers for Disease Control and Prevention (CDC) have recommended discontinuing the Western blot test.
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.
Testing and diagnosis are an important part of staying healthy with HIV. With early diagnosis, early treatment is possible. Testing is the first step in accessing effective ways of managing the condition. It is the key to both treatment and prevention.
Current treatment can reduce the viral load to undetectable levels. While levels are this low, the body can remain healthy, the individual can expect a normal lifespan, and the virus cannot be transmitted.
Explaining the tests
The ELISA test is a blood antibody test that checks for proteins the body makes if HIV is present.
Laboratory blood tests can be used to diagnose HIV through detecting certain antibodies or proteins produced by the immune system in response to the virus.
The ELISA test, also called the EIA for enzyme immunoassay, is used to detect the HIV antibody. It checks for certain proteins that the body makes in response to HIV.
The blood sample will be added to a cassette that contains the viral protein, called antigen.
If the blood contains antibodies to HIV, it will bind with the antigen and cause the cassette's contents to change color. This very sensitive test was the first one widely used to check for HIV.
The Western blot test was previously used to confirm the result of the ELISA, but it is no longer recommended, as other tests are now more reliable and enable a faster diagnosis.
In the Western blot test, the blood is taken in the same way, but 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.
Who has the tests?
Most adults will undergo screening at some time. It is a routine procedure during pregnancy.
However, the Western blot and ELISA tests are only recommended if a person may have been exposed to HIV.
People with a high risk of exposure include:
- those who have sex without using a condom, especially with someone who has HIV
- those who share needles
- 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, for example, if they have a new sexual partner or work in healthcare situations.
Tests are conducted by taking a blood sample.
There is no special preparation for the ELISA test. It is a simple blood test.
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 these tests.
When using the ELISA test for HIV screening, it is important to be aware of the window of exposure. If the ELISA test is done too soon after exposure, the body will not have produced enough antibodies to cause a positive result, even though the virus may be present.
What to expect: Before, during, and after the tests
The ELISA test is a standard blood 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, 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 person 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 of a single test will not be simply positive or negative.
This is why a second test is needed to confirm the results.
Because the ELISA test is extremely sensitive, some people may test falsely positive.
Because of this, positive ELISA test results need to be confirmed through another test.
However, if both the ELISA test and another test both detect the virus, it is likely to be present.
What happens next depends on the results of the tests.
What happens if the result is negative?
The results of both tests are negative: If exposure happened within the last 3 months, HIV might be present but not yet detectable. In this case, a person should repeat testing in 3 months. Meanwhile, they should take precautions to prevent transmission of the virus, just in case.
The result is negative, and the person has not had exposure to HIV: No further testing may be needed.
What if the result is positive?
One or both test results are positive: It is crucial to seek medical help immediately. Further testing may be recommended to confirm the result, and a treatment regime can be started if necessary.
This may include:
- a prescription for antiretroviral medications
- information about where to go for specialist treatment
- advice about local support groups
- recommendations for preventing transmission
Tests and results are usually confidential and sometimes anonymous. However, it if the result is positive, it is important to talk to a partner about this, as screening may be advisable for them, too.
Financial help is available for treatment of HIV. Insurers are required to cover some of the costs, and government health programs may be able to help those who do not have insurance.
Many types of HIV test are available and recommended for laboratories to use.
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.
Home testing kits are available for purchase online. It is important to check that the kit is approved by the United States Food and Drug Administration (FDA) and to follow all the instructions carefully.
If the result is positive, the person will need ongoing support. It is important to keep all appointments and to follow the health team's advice with care.
Further tests and monitoring will be carried out at intervals or as needed.
A CD4 count can help keep track of how well the immune system is working and the likelihood of contracting an opportunistic infection or disease over time.
A viral load test shows how much virus is in the blood. When the viral load is below a certain level, it is undetectable. As long as it remains undetectable, the person can expect to remain healthy, and they will not transmit the virus to another individual.
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