With the emergence of at-home HIV self-testing kits, advanced HIV testing technology, which was once accessible only in a clinical setting, has been made available for use in the privacy and comfort of one’s own home.
Up until recently, however, at-home HIV tests were mostly using 3rd generation assays, which are only able to detect HIV antibodies; nowadays, more advanced 4th generation tests, which screen for both antibodies and antigens, are also increasingly available as at-home self-testing kits.
The 4th generation of HIV tests is also referred to as ‘combination/combo/DUO tests’ or ELISA (short for ‘enzyme linked immunosorbent assay’). With many countries moving away from 3rd gen toward 4th and 5th gen testing in clinical settings, the arrival of 4th generation technology in a compact, DIY format is widely hailed as a revolution in HIV diagnostics.
But what exactly does this improved testing ability entail and why is it significant in the bigger picture? Read on to find out.
HIV testing has developed dramatically since its somewhat chaotic beginnings in 1985. In the almost four decades that have since passed, we’ve made significant progress in testing technology, but also in the treatment of HIV, which is now able to drastically reduce symptomatology and mortality in infected individuals.
As a result, the stigma toward HIV testing and the illness itself has mostly dissolved, while much more convenient, rapid, and discreet testing options, such as at-home HIV self-testing kits, have become widely available on the market.
Still, although at-home HIV tests are highly reliable, most of them are based on 3rd generation testing technology, meaning that they analyze the provided sample (blood or saliva) for the presence of HIV antibodies.
Tests that screen for antibodies need a sufficient level of antibodies created by the immune system of the infected person in order to be able to reliably detect them; this can happen anywhere between 3 weeks and 3 months after contracting the virus.
This period in between infection and reliable detection is likely the most important aspect of HIV testing and, therefore, suppression. It’s referred to as the ‘window period’ and it depends on two factors:
All this is to say that, while 3rd generation tests (especially when available in an affordable at-home self-testing format) are immensely helpful in HIV diagnostics, they need at least 3 weeks to pass after infection to be able to even remotely provide accurate results, and 3 months for total reliability.
On the other hand, 4th generation HIV tests screen for both antibodies and antigens; why this is so consequential is because antigens are produced before the antibody response is even initiated, and they are already detectable between 13 and 24 days post-infection (18 days being the median).
Even more encouragingly, the position of sexual healthcare providers of certain Western countries, such as the UK, is that a combo (4th gen) test result can already be considered conclusive 28 days post-exposure, a moment at the tail end of the peak range of antigen levels in an infected person (between 20 and 30 days).
In parallel with acute HIV symptom onset, which typically happens between 2 to 4 weeks post-infection, HIV antigens (viral proteins) grow in numbers as the viral particles rapidly multiply. During this time, the infected person’s immune system is yet to mobilize its defenses against the attack.
The key antigen that 4th generation HIV tests screen for is p24 — a major structural protein of the HIV virus. This vital component of the HIV conical core encloses the viral genome and is, therefore, responsible for the assembly and stability of the HIV capsid.
Once the immune system of the infected individual starts the process of seroconversion — the creation of antibodies which aim to damage, neutralize, or kill the viral particles — the antibodies bind to the p24 antigen, forming immune complexes. This process interferes with p24 assay detection, gradually reducing its viability until antigens can no longer be detected (at about 6 weeks post-infection).
This all means that by screening for both antigens and antibodies, like 4th generation HIV tests do, the infection can be discovered at least one week earlier than with tests that screen for antibodies alone. Then, during the period of overlap of antibodies and antigens, it provides double reliability by screening for both. Finally, once the antigens can’t be picked up by the assay anymore, high levels of antibodies are left for reliable detection.
The implication of this decreased ‘window period’ and enhanced reliability is that, if 4th generation HIV tests can become the standard in at-home testing practices as they have in clinical settings, we can significantly elevate the global percentage of early HIV detection, reduce unintentional transmission, and witness great improvements in HIV treatment with early therapy applied more often.
Aside from their ability to detect HIV earlier and more reliably, 4th generation at-home HIV tests have several advantages over other HIV testing methods (including clinical ones):
Comfort: At-home testing kits offer a convenient, discreet way for anyone to test for HIV in the comfort of their own home, without having to visit a healthcare provider or clinic. This can be particularly beneficial for those who may feel uncomfortable or stigmatized when seeking testing services in a clinical setting.
Accuracy: 4th generation at-home HIV test kits are as accurate as clinical tests, which have been reported by the CDC to have relative sensitivity (true positives) of over 99.7% up to 99.9% and relative specificity (true negatives) of 99.5% or above. This means that false positive and false negative results are very rare, and that those seeking to get tested can have almost complete confidence in their results.
Value: Because they don’t require the same level of resources or infrastructure as clinical testing methods, at-home testing kits are generally more cost-effective. This can make HIV testing more accessible to those living in environments without sufficiently developed healthcare services or those unable to afford clinical testing, where it is costly.
Although 4th generation at-home HIV testing kits offer a convenient and discreet way to learn your HIV status rapidly and reliably, they also have some limitations that should be considered:
Indirect HIV detection: Because 4th gen combo tests screen for HIV antigens and antibodies, they are able to detect the presence of the virus only indirectly, meaning that, even if the infection exists, it might not be picked up during the ‘window period’ because the tests don’t screen for the viral particles themselves. This cannot be considered a flaw, but rather a constraint, as even the most sophisticated laboratory tests, which can directly detect parts of the HIV genetic code (NATs), can only pick up the presence of the virus 10 days post-exposure at the earliest.
Need for follow-up testing: While 4th generation at-home HIV tests are more accurate than previous generation tests, they are not infallible. If you receive a positive result, you will need to follow up with confirmatory testing at a medical facility or clinic.
Potential for error: There is always the possibility that the sample added to the testing cassette may become contaminated in the process of collection, or that the testing kit itself may be defective. To reduce the probability of human error, it is important to follow the provided instructions carefully to ensure that the sample is collected and processed correctly. In the case of a defective testing unit, reach out to us to receive a free replacement.
All in all, at-home 4th gen HIV self-testing kits are the peak of our achievement in setting-independent HIV testing. They provide affordable, rapid, highly reliable results (provided they are employed after the ‘window period’), while circumventing the stigma or sometimes complicated logistics of clinical testing.
With many advantages and very few drawbacks, 4th gen tests are a must-have tool for anyone at increased risk of HIV or with an interest in regular tracking of their sexual health.
Order a 4th Generation At-Home HIV Self-Testing Kit today