Let's face it: you're not going to be worried about your HIV status for very long. You'll probably get tested before the 3 months are up, or even just after one, but it's still important to know how reliable your test results are. And that depends on what kind of test you take — in this case, there are two types of tests that can tell if you have HIV:
P24 antigen test
4th generation rapid antibody test
The fourth generation HIV test is the most accurate test for detecting HIV antibodies. The accuracy of this test after 28 days is 99.2%. This means that if you are negative on this test, you are almost certainly negative (99.2% chance). And if you are positive on this test, then there's a 99.2% chance that your getting an accurate result and your infection is recent (28 days or less).
The big caveat here is that it takes about 3 months for antibodies to develop in the body which means that if you got tested more than 28 days ago, there may not be enough antibodies in your blood sample to give a conclusive result. If this happens then they will likely recommend repeating the test again after another 3 months or so when there should be enough antibodies present in your blood stream
The p24 antigen test is the most accurate and reliable test. It's also the most expensive, so if you're not sure how reliable your results are, don't bother with this one just yet.
The p24 antigen test is an enzyme-linked immunoassay (ELISA) that detects HIV antibodies in your blood sample. In other words, it looks for evidence of infection based on antibodies produced by your immune system when fighting off HIV. This type of testing is usually used to confirm a negative result after initial testing has been done with another method such as home kits or rapid tests that can detect viral load more quickly but aren't always as accurate in determining whether someone has HIV or not
In general, the test is accurate. But there are some cases that this might not be true in some individuals, or if someone has a weak immune system.
In these cases, you should get a follow-up test to make sure the result is correct and then go ahead with treatment accordingly.
If your test results are negative and you have not had any high risk exposure since your last possible exposure, you are good to go! You can also be confident that you're negative if:
You can know for sure that you're negative in 4 weeks for almost everyone. After this time, the chance of getting a false positive is very low. However, it's still possible to get a false positive result after this period if you have been infected with HIV but your immune system hasn't produced enough antibodies to show up on the test. This is more likely to happen in people who have been recently infected with HIV or have other conditions such as an autoimmune disease or infection with another virus like hepatitis C or herpes simplex virus type 1 (HSV-1).
The 4th generation HIV test can detect p24 antigen, a part of the surface of the virus that is produced long before antibodies are made to fight it. Antibodies are made in response to antigens being produced by viruses. In this case, antibodies do not appear until after p24 antigen is present on your body's cells.
Antigens are molecules that trigger an immune response when they come into contact with cells in our bodies. They're not antibodies (which are proteins). The difference between them is simple: Antigens don't have genetic information like most other molecules do; they're just bits of protein or other material that cause our immune systems to react as if they were viruses or foreign invaders of some sort.
The window period, or the time between when a person is infected with HIV and when they develop antibodies against HIV in their blood that can be detected by an HIV test, is 18-21 days. This means that if you have had unprotected sex during this window period with someone who may have been infected with HIV (though we do not know for sure), there is a chance that the 4th generation p24 antigen/antibody test would not detect your antibodies immediately after exposure.
The 4th generation tests are 99% accurate at 28 days after exposure and 100% accurate at 32-35 days after exposure.
If you are concerned that your 4th generation HIV test might not have been conclusive, the CDC recommends retesting with a PCR viral load test. A PCR test is an expensive and time-consuming test that is usually only ordered when there is reason to believe that the 4th generation HIV test might not be conclusive, such as if other factors were suspected of affecting your results. The cost of this type of testing can range anywhere from $300 to $2,000 depending on what kind of lab you use and how far away from you they are located. For example, some private labs charge around $600 for this type of analysis while others charge as high as $1,800 for it. If insurance covers this type of analysis for patients who have received their 4th generation HIV results within the past three months then it may be worth contacting your health plan directly before making any decisions about retesting yourself.
If someone needs an HIV test after 32 days, the standard antibody/antigen 4th generation HIV test is considered conclusive at this point in time.
For example, if a person tests negative for HIV antibodies on day 31 and then has sex with another individual and experiences symptoms of acute retrovirus infection on day 36, we would want to know whether or not this person has contracted HIV from their last sexual encounter. If they have tested positive for both anti-gp120 and p24 antigen by PCR (polymerase chain reaction), this would suggest that they were indeed infected recently and should be advised that there is no need for further testing.
If your doctor recommends an additional test after the standard antibody/antigen 4th generation HIV test, ask why it’s necessary — it may seem unnecessary at first glance but could keep you safe! You can also take precautions against contracting STIs by using condoms every time you have sex and getting tested regularly as well as practicing safer sex habits like limiting the number of partners and always using protection when having unprotected intercourse so that you don't end up with a case of paranoia about contracting any sexually transmitted diseases including genital warts which can cause permanent scarring if left untreated.
I hope this information was helpful! If you have any additional questions, please let me know.