You've had unprotected sex with someone and you're worried that you might have contracted HIV. You've gone to the doctor, who has taken an oral swab and sent it off for testing. The results are back, and they're negative. What does that mean? This article will help explore how conclusive a third-generation HIV test after nine weeks is, along with what other options may be available if you still want to get tested further down the road (or don't trust your doctor's opinion).
A third-generation HIV antibody test looks for a variety of HIV antigens, not just antibodies. Antigens are proteins on the surface of the virus that can be detected up to three months after infection, whereas antibodies can be detected up to nine weeks after infection.
Many in the medical community consider this test conclusive after three months because it detects P24 antigens and antibodies.
P24 is a protein produced by HIV, which can be detected in the blood for about three months after possible exposure to HIV. But because P24 levels are so low at this point that they're hard to detect, doctors recommend waiting until you've been exposed for at least three months before taking the test.
In case you're wondering, there is a rapid HIV test that is considered conclusive after three months.
Rapid HIV tests are available as an alternative to antibody testing. They can give you the results in 20 minutes or less and they can be performed at home or in a doctor's office. They work by detecting the presence of anti-HIV antibodies in your blood and are extremely accurate (99%).
In clinical trials, it was found that if a person using a rapid test had their initial negative result at nine weeks but then tested positive on further antibody testing at 12 weeks, there would be about a 10% chance that this was due to a false negative result from their rapid test at 9 weeks - meaning their body had not yet produced enough antibodies for the first rapid test to detect them.
As a general rule, you should test for HIV as soon as possible after a potential exposure. However, there are some situations in which it's not advised to test right away. For example, if you've recently been exposed to the virus and haven't had any symptoms yet, but want to see if your body has produced antibodies against HIV antibodies (which is what the 3rd generation test looks for), testing in the first weeks after possible exposure can yield a false negative and isn't recommended.
If you do wait two or three weeks before getting tested for HIV at nine weeks after possible exposure and your result comes back negative, that means that either: A) You don't have antibodies against HIV on board yet; or B) Your immune system has already made them but hasn't produced enough of them yet for the test to pick up on them
Most doctors recommend that you wait until three months after your possible exposure to get tested. The reason for this is because the third-generation test can detect HIV antibodies in your blood as early as 30 days after exposure, and these antibodies will continue to grow over time. So at three months, if the antigen test (used in first generation tests) comes back negative but you still have high levels of antibodies, it's likely you'll get a positive result on a second test.
However, some doctors recommend waiting even longer before taking an antibody test — up to six months after exposure. This recommendation is based on research suggesting that people who have been infected with HIV might take longer than average to produce enough antibodies for detection by third-generation tests. The CDC says this recommendation may apply more often among adults who have sex with men than among those who don't engage in sexual behaviors involving risk of HIV infection (such as unprotected vaginal intercourse).
A third-generation HIV test detects both antibodies and the p24 antigen. An antibody is a protein produced by the body's immune system to fight infection. The p24 antigen is found inside cells infected with HIV and is used to detect early infection in the first few weeks after infection occurs.
A fourth-generation test detects only antibodies and does not detect p24 antigens, so it can be used for screening when you're between 3 and 12 weeks since exposure (or 14 days after last possible exposure).
The third-generation HIV test detects HIV antibodies and p24 antigen. It can detect an HIV infection at 3 weeks, 4 weeks, and 5 weeks after the exposure.
A 3rd generation test is able to detect antibodies, the immune proteins that your body produces in response to infection. For most people, it takes approximately 2-8 weeks for these antibodies to appear after an HIV exposure.
However, even if a person shows positive on a third-generation test, this does not necessarily mean that they have been infected with HIV. It's possible for someone who was initially exposed but has not produced detectable amounts of antibodies yet to still get a false positive result from their HIV test. If you think you might have been exposed, it's best to wait 12 weeks before testing again (which will allow enough time for your body's immune system to create antibodies).
The earliest time you can test for HIV is 21 days after exposure. This is the earliest that people with a positive result will have detectable antibodies in their blood. Most people will have detectable antibodies by 25 days after exposure, but it can take up to three months or longer before they develop detectable antibodies.
The reason why 25 days is a conservative number is because the immune system responds to infections by producing antibodies, which can be detected by a test after 21 days. However, the immune system does not generate enough antibodies in this time frame for them to be detected with certainty in your blood sample. It takes about 1-2 months for your body to develop enough antibodies that can be counted as HIV positive (or negative). So if you get tested at 9 weeks and your results are negative, it’s unlikely that they will change over time. This means you can feel confident about those results!
The probability of infection drops significantly after 8 weeks. However, it is still possible to be infected and not test positive until later. It's important to remember that a 3rd generation HIV test is an initial screen and does not give you absolute certainty about your status. A negative result means that you are very unlikely to be infected with HIV virus but a positive result does not mean that you definitely have HIV infection. For complete certainty, you should repeat the test again in 12 weeks or ask your doctor for advice on how long to wait before taking another one-off test (see How do I know when I'm HIV negative?).
The most important thing is that you get tested for HIV and other STIs regularly. If you haven't had an HIV test, or if it's been more than three months since your last one, go get tested now! You can find a clinic near you through our directory.