HIV test – When is the best time to do it?
What is HIV?
HIV infection in humans came from a type of chimpanzee in Central Africa. The chimpanzee version of the virus (called simian immunodeficiency virus, or SIV) was probably passed to humans when humans hunted these chimpanzees for meat and came in contact with their infected blood. Studies show that HIV may have jumped from chimpanzees to humans as far back as the late 1800s. Over decades, HIV slowly spread across Africa and later into other parts of the world. We know that the virus has existed in the United States since at least the mid to late 1970s. How do I know if I have HIV?
The only way to know for sure whether you have HIV is to get tested. Knowing your HIV status helps you make healthy decisions to prevent getting or transmitting HIV. This is why HIV testing is essential.
When is the best time to do the HIV test?
There are a variety of HIV test available, depending on the length of exposure.
In summary, here are the tests you can do at the appropriate time:
Day 1-3: Consider Post-Exposure Prophylaxis (PEP)
Day 1-11: No HIV testing available
Day 12 onwards: HIV RNA/DNA PCR testing
Day 14 onwards: 4th Generation Combo testing can start to pick up the infection (may have a false negative)
Day 28 onwards: 4th Generation Combo testing is deemed conclusive
Day 90 onwards: 3rd Generation Ab-only testing is deemed conclusive
Should I get tested for HIV?
1) Are you a man who has had sex with another man?
2) Have you had sex—anal or vaginal—with a partner who has HIV?
3) Have you had more than one sex partner since your last HIV test?
4) Have you injected drugs and shared needles, syringes, or other drug injection equipment (for example, cookers) with others?
5) Have you exchanged sex for drugs or money?
6) Have you been diagnosed with or treated for another sexually transmitted illness
7) Have you been diagnosed with or treated for hepatitis or tuberculosis (TB)?
8) Have you had sex with someone who could answer yes to any of the above questions or someone whose sexual history you don’t know?
You should be tested at least once a year if you keep doing any of these things. Sexually active gay and bisexual men may benefit from more frequent testing (for example, every 3 to 6 months). If you’re pregnant, talk to your health care provider about getting tested for HIV and other ways to protect you and your child from getting HIV.
What should I expect when I go in for an HIV test?
What kinds of tests are available, and how do they work?
There are three types of tests available: nucleic acid tests (NAT), antigen/antibody tests, and antibody tests. HIV tests are typically performed on blood or oral fluid.
1) NAT / PCR
These test looks for the actual virus in the blood and involves drawing blood from a vein. The test can either tell if a person has HIV or tell how much virus is present in the blood (known as an HIV viral load test). While a NAT can detect HIV sooner than other types of tests, this test is very expensive and not routinely used for screening individuals unless they recently had a high-risk exposure or a possible exposure and have early symptoms of HIV infection.
2) 4th Generation HIV antigen/antibody test
Looks for both HIV antibodies and antigens. Antibodies are produced by your immune system when you’re exposed to viruses like HIV. Antigens are foreign substances that cause your immune system to activate. If you have HIV, an antigen called p24 is produced even before antibodies develop. Antigen/antibody tests are recommended for testing done in labs and are now common in the United States. This lab test involves drawing blood from a vein. There is also a rapid antigen/antibody test available that is done with a finger prick.
3) 3rd Generation HIV antibody tests
Only look for antibodies to HIV in your blood. In general, antibody tests that use blood from a vein can detect HIV sooner after infection than tests done with blood from a finger prick or with oral fluid.
How long does it take to get results?
Laboratory tests (NAT and antigen/antibody) require blood to be drawn from your vein into a tube and then that blood is sent to a laboratory for testing. The results may take several days to be available.
4th Generation Rapid Antigen/Antibody Test is done with a finger prick and takes 30 minutes or less.
Can I detect HIV directly after high risk sexual encounter?
If you get an HIV test after a potential HIV exposure and the result is negative, get tested again after the window period. Remember, you can only be sure you are HIV-negative if:
1) Your most recent test is after the window period.
2) You haven’t had a potential HIV exposure during the window period. If you do have a potential exposure, then you will need to be retested.