The fourth generation tests can identify both HIV-specific antigen p24 and HIV antibodies with a blood sample.
The fourth generation HIV test, also called an enzyme-linked immunosorbent assay (ELISA) test, is a more complete screening that can identify acute HIV. This is the time when the virus is multiplying rapidly and you’re more likely to pass the infection.
In the first few weeks after exposure to HIV, your body produces an antigen known as p24. This protein is only present in people who have acute HIV infection. It triggers your immune system to respond.
The fourth generation tests require a blood sample that’s sent to a lab for testing. Blood testing done by a lab is the most accurate type of test.
There are several types of tests that can test for the presence of HIV. HIV testing can be done by drawing blood from a vein, a finger stick, or taking an oral swab of fluid.
Tests can measure antibodies, antigen/antibody (fourth generation), and there’s also a nucleic acid test (NAT). The NAT test can identify HIV and viral load (amount of virus in the blood). It can tell if you have HIV within around 10 to 33 days of exposure.
Older generation HIV tests and home test kits can’t detect acute HIV because they only detect antibodies produced by your immune system. Antibodies to HIV aren’t produced until several weeks after exposure.
Older tests like the third generation tests aren’t reliable until about 3 months after exposure to the virus.
This can delay getting treatment if you’re positive and increase the risk of passing the virus unknowingly. An estimated 40 percent of new HIV infections are transmitted by those who don’t know they’re positive for HIV.
The fourth generation test is different because it’s a combination test that’s more advanced. It can detect both HIV antibodies and the p24 antigen, which is associated with HIV. Testing for p24 allows earlier detection and diagnosing of acute HIV infection.
For a fourth generation test, you’ll have a small sample of blood drawn from a vein with a needle. You might feel a small sting from the needle. It takes a few minutes to take the sample. Once the sample is collected, it’ll be tested in a lab.
You can get a false positive HIV test. This is when a person who doesn’t have HIV tests positive.
Newer tests like the fourth generation test are more accurate, but false positive and false negative (testing negative when you have HIV infection) results can happen for many reasons.
False positive results can happen if:
- the testing sample is contaminated
- the lab misreads or mislabels the test
- you’ve been part of a HIV vaccine study
Keep in mind, testing blood versus saliva may also affect accuracy of results.
What is HIV?
HIV (human immunodeficiency virus) is a virus that attacks your immune system. It’s transmitted through blood, semen, breast milk, and vaginal and rectal fluids. Early testing is a crucial step toward treatment and reducing transmission.
There’s no cure for HIV, but many medications are available both for prevention and treatment. New treatments are allowing people to live longer with an undetectable viral load. This means that the virus can’t be detected in the blood by lab tests.
HIV Ag/Ab, 4th Gen
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