Since the early days of the HIV epidemic, HIV tests have improved considerably. We now have multiple methods to test for HIV infection, and today’s testing technologies are getting better at detecting new infections. This has led some HIV testing experts to suggest that we can detect the vast majority of HIV infections much earlier than many people realize.
Did you know a home test is available that can give you a result within 20 minutes?
The test uses an approved oral test method that detects antibodies to HIV in cells from your mouth. It is easy, convenient, and reliable. A swab is rubbed along the gums to get an oral fluid sample, which is then immersed in a reaction solution, and the result is available after 20 minutes. Note: an oral fluid sample that can be tested for HIV contains cells from your mouth. It’s different from saliva.
In short, how long does HIV take to show up on a test?
- Antigen/Antibody Test—A laboratory antigen/antibody test performed on blood from your vein can usually detect HIV infection 18 to 45 days after exposure.
- An antigen/antibody test done with blood from a finger prick takes longer to detect HIV (18 to 90 days after exposure).
Why is it valuable to detect HIV infections as early as possible?
There are two significant reasons why it is valuable to detect an HIV infection as soon as possible after it has occurred:
Early detection is best for people getting tested for HIV. HIV tests that provide an accurate result sooner after infection may significantly reduce the anxiety of “not knowing” that many people feel after they think they may have been exposed to HIV.
For those who test HIV-positive, testing early may give them a better sense of how and when they were exposed to HIV. It may also give them greater opportunities to access services and support that will help manage their health and well-being. Another distinct advantage of early diagnosis is that people can access anti-HIV treatment before their immune systems have been severely damaged, which can also improve their long-term health outcomes and help prevent HIV transmission.
In fact, the evidence for sexual transmission shows that people on ART who maintain an undetectable viral load do not pass HIV to their sexual partners.
Early detection can help prevent new HIV infections. Research demonstrates that almost half of new HIV infections may come from individuals who have been newly infected. This may be because people who are freshly infected have significantly higher levels of the virus in their blood and genital tracts, which may make HIV transmission more likely to occur. People who are newly infected are also more likely to be unaware of their HIV status. Diagnosing HIV infection early allows a person to make more informed decisions (such as practising safer sex and using drugs more safely). Research shows that when aware of their status, most HIV-positive people do take steps to prevent HIV transmission.
Being able to detect new HIV infections earlier is beneficial not only to people seeking testing but also to the service providers offering testing services. Still, it may also play a significant role in preventing further transmission of HIV within the population.
HIV testing should be voluntary, and the right to decline testing should be recognized. Mandatory or coerced testing by a healthcare provider, authority, partner or family member is unacceptable as it undermines good public health practise and infringes on human rights.
Some countries have introduced or are considering self-testing as an additional option. HIV self-testing is a process whereby a person who wants to know his or her HIV status collects a specimen, performs a test, and interprets the test results in private. HIV self-testing does not provide a definitive diagnosis; instead, it is an initial test that requires further testing by a health worker using a nationally validated testing algorithm.
All HIV testing services must include the 5 C’s recommended by WHO: informed Consent, Confidentiality, Counselling, Correct test results and Connection (linkage to care, treatment and other services).
If you think you may have been exposed to HIV, get an HIV test. Most HIV tests detect antibodies (proteins your body makes against HIV), not HIV itself. However, it takes a few weeks for your body to produce these antibodies, so if you test too early, you might not get an accurate test result. A new HIV test is available that can detect HIV directly during this early stage of infection. So be sure to let your testing site know if you think you may have been recently infected with HIV.
What kind of tests are there?
Rapid HIV diagnostic home-kit tests are available, but these tests should be used with extreme care. Doing the home test without proper pre-test and post-test counselling is not advisable. The results can also be incorrect if the testing instructions are not followed precisely if the test has not been stored at the required temperature, if the test expiration date has been exceeded, or if tests of low quality are used. A subsequent laboratory test should always confirm a positive result from a home test. HIV self-tests are already available in some pharmacies for about R 75.
A rapid HIV antibody test is a blood test which can be done by pricking the finger with a lancet and applying the test tube. The result is ready within 15 minutes.
Rapid tests are beneficial for the diagnosis of HIV infection in rural or isolated areas that are far removed from diagnostic laboratories and where clients often cannot afford to come back for test results.
These tests are relatively cheap and demonstrate a high-reliability rate if they are correctly used.
Once a person becomes infected with HIV, several steps must take place before an HIV antibody test can detect infection.
- First, the virus infects more and more cells in the person’s body.
- The person’s immune system then responds by producing HIV antibodies, proteins that circulate in the blood to fight the HIV infection.
- It is these antibodies that the HIV antibody test detects, NOT HIV itself.
- If there aren’t enough antibodies created by the body when the test is given, the result will be negative despite the person being infected with HIV.
For an HIV antibody test to detect an HIV infection, two conditions must be met:
HIV antibodies must be present in the person’s blood. The amount of time it takes for the immune system to create HIV antibodies after HIV infection varies
- based on genetics,
- how transmission occurred (e.g. sex vs. shared needles),
- the amount of virus the person was exposed to,
- whether they underwent post-exposure prophylaxis (when someone takes a combination of anti-HIV medications within 72 hours of exposure to reduce the chances of becoming infected), and numerous other factors.
For more on PEP, see Can we prevent infection with HIV after an exposure?
The HIV antibody test must be sensitive enough to detect the antibodies. Newer testing technologies can now detect HIV antibodies when there are lower concentrations in the blood and hence detect an HIV infection much sooner.
The “window period” refers to the maximum amount of time it may take for a person’s body to create HIV antibodies after HIV infection. HIV antibodies must be present for the HIV antibody test to detect HIV antibodies in someone’s blood accurately. If someone is “in the window period,” there is a chance that even though they may have been infected with HIV, the test won’t be able to detect the infection and will give a negative result.
HIV antibody tests are the most widely used HIV tests. One of the main reasons they are so widely used is that once HIV antibodies are present in a person’s blood, they will be there for the rest of that person’s life (provided their immune system is functioning correctly). This means that following the window period, an HIV antibody test will always give a positive result for someone who has been infected with HIV. This is important as many people are not diagnosed until several years after infection.
Older HIV antibody tests were significantly less able than newer tests to detect low levels of HIV antibodies in a person’s blood, which is why, in the past, the window period was set at six months.
Research shows us that with these new tests, as many as 95% of people who test positive will do so within 34 days of exposure to HIV. However, for the remaining 5%, the window period for these HIV antibody tests is generally accepted to be three months to ensure people who take longer to develop antibodies are not overlooked. This means that if someone tests negative for HIV antibodies during the window period, they should be re-tested three months after possible exposure to entirely rule out HIV infection.
Some rare exceptions may require someone to retest up to six months after exposure:
People who have a severely impaired immune system may take longer to develop HIV antibodies.
People who have taken post-exposure prophylaxis (PEP). This is a one-month course of anti-HIV drugs that, if started within 72 hours of potential exposure, may reduce the risk of HIV infection. If PEP does not successfully prevent HIV infection in someone, the presence of the PEP drugs may still reduce HIV replication until the medicines are finished. This may delay the time it takes for a person’s body to create HIV antibodies.
Tests that directly detect HIV
Several technologies detect HIV itself. It is essential to do some research and find out which testing services are available for your clients to help ensure effective messaging for someone who thinks they have recently been exposed to HIV.
The two most commonly used tests that detect HIV directly are the p24 antigen test and the HIV nucleic acid amplification test (NAAT).
- The HIV p 24 antigen test, the most widely available of the two, is designed to detect a protein (the p 24 protein) associated with HIV. The p 24 antigen test can detect the p 24 protein on average 10 to 14 days after infection with HIV. One drawback of this test is that levels of the p 24 protein peak at around three to four weeks after exposure to HIV and are usually not detectable after five to six weeks (and sometimes even earlier). A positive p-24 test means that someone is HIV-positive. However, a negative p-24 test can mean three things:
- the person is HIV-negative
- the person is HIV-positive, but the test could not detect the p-24 protein because the person was infected more than four to six weeks earlier
- the levels of the p-24 antigen are too low to be detectable with current technologies.
The most advanced tests combine a p-24 antigen test and an antibody test. These tests are seen as beneficial because they combine the early detection abilities of the p-24 antigen test with the accuracy of the newer antibody tests. It should be noted that a rapid (point-of-care) version of these tests is not yet available.
The HIV NAAT (Nucleic acid amplification techniques) test is a susceptible test designed to detect HIV RNA in blood. RNA is the viral equivalent of human DNA. The NAAT test can detect HIV RNA as early as seven to 14 days after infection with HIV. Unlike the p24 test, the NAAT test will always give a positive result as long as there is HIV in someone’s blood.
Seroconversion symptoms
It is also important to talk about the symptoms of seroconversion when we talk about testing.
Seroconversion is the interval, several weeks after HIV infection, during which antibodies are first produced and rise to detectable levels.
Antibodies generally begin to appear within one to two weeks of exposure, and antibody concentrations (titres) continue to increase for several months after that. In most infected individuals, seroconversion takes place within three weeks, although sporadic cases are reported in which seroconversion does not occur for up to a year.
Seroconversion is often – although not always – accompanied by a flare of symptoms called seroconversion illness (sometimes also called acute retroviral syndrome). Symptomatic seroconversion illness occurs in at least 50%, and possibly as many as 80 or 90%, of infected individuals. The symptoms can appear two to four weeks after infection and may include flu-like symptoms, such as fatigue, fever, sore throat, swollen lymph nodes, headache, loss of appetite or skin rash. This illness usually lasts less than two weeks, although it can last as long as ten weeks. Educating clients about the symptoms of seroconversion may increase the likelihood that they will get tested if they experience symptoms.
If a client has had a recent high-risk encounter and experiences any of these symptoms, they should be encouraged to have an HIV test. The antibody test may not give an accurate result depending on the time of infection. However, if available, the p 24 antigen test will be able to give a precise result two to four weeks following infection, and the NAAT test will be correct in as little as seven to 14 days after infection.
What does all this mean for front-line workers?
The early detection of HIV is important because people who are newly infected are very infectious and may inadvertently transmit HIV to others. There is still a lot of misunderstanding about how soon one should get tested after potential HIV exposure. Many people still believe they have to wait three months. However, new and improved testing technologies are continually decreasing the amount of time it takes for a new HIV infection to be detected.
In the case of clients at high risk of HIV, testing can be done as early as one month after exposure for standard antibody assays and rapid point-of-care tests. Clients who test positive will know for sure they are HIV-positive. Of those who test negative, 95% are negative. It is essential to realize that up to 5% of people who test negative at one month could later test positive at three months. It is crucial to ensure that people testing negative at one month are advised to return for repeat testing once the three-month window period is covered.
