At this level within the pandemic, you or somebody has in all probability obtained at the least one COVID-19 take a look at. However are you aware which form of take a look at you bought and the strengths and weaknesses of those totally different assessments?
I’m a molecular biologist, and since April 2020 I’ve been a part of a staff engaged on a Nationwide Institutes of Well being-funded program referred to as RADx that’s serving to innovators develop speedy assessments to detect when an individual is contaminated with SARS-CoV-2, the virus that causes COVID-19.
Two main varieties of assessments are used to diagnose an infection with SARS-CoV-2: molecular assessments – higher generally known as PCR assessments – and antigen assessments. Every detects a distinct a part of the virus, and the way it works influences the take a look at’s velocity and relative accuracy. So what are the variations between all these assessments?
Karl Mumm through Wikimedia Commons, CC BY-SA
On the lookout for genetic proof
Step one for both form of take a look at is to get a pattern from the affected person. This is usually a nasal swab or a little bit of saliva.
For PCR assessments, the following step is amplification of genetic materials in order that even a small quantity of coronavirus genes within the affected person’s pattern may be detected. That is finished utilizing a way referred to as a polymerase chain response. A well being care employee takes the pattern and treats it with an enzyme that converts RNA into double-stranded DNA. Then, the DNA is combined with an answer containing an enzyme referred to as a polymerase and heated, inflicting the DNA to separate into two single-stranded DNA items. The temperature is lowered, and polymerase, with the assistance of a small piece of information DNA referred to as a primer, binds to the single-stranded DNA and copies it. The primers be certain that solely coronavirus DNA is amplified. You’ve now created two copies of coronavirus DNA from the unique one piece of RNA.
Laboratory machines repeat these heating and cooling cycles 30 to 40 occasions, doubling the DNA till there are a billion copies of the unique piece. The amplified sequence accommodates fluorescent dye that’s learn by a machine.
The amplifying property of PCR permits the take a look at to efficiently detect even the smallest quantity of coronavirus genetic materials in a pattern. This makes it a extremely delicate and correct take a look at. With accuracy that approaches 100%, it’s the gold commonplace for diagnosing SARS–CoV–2.
Nonetheless, PCR assessments have some weaknesses too. They require a talented laboratory technician and particular tools to run them, and the amplification course of can take an hour or extra from begin to end. Normally solely giant, centralized testing amenities – like hospital labs – can conduct many PCR assessments at a time. Between pattern assortment, transportation, amplification, detection and reporting, it may well take from 12 hours to 5 days for an individual to get outcomes again. And eventually, they aren’t low-cost at $100 or extra per take a look at.
Lennardywlee through Wikimedia Commons, CC BY-SA
Speedy, correct assessments are important to include a extremely contagious virus like SARS-CoV-2. PCR assessments are correct however can take a very long time to provide outcomes. Antigen assessments, the opposite main sort of coronavirus take a look at, whereas a lot sooner, are much less correct.
Antigens are substances that trigger the physique to provide an immune response – they set off the technology of antibodies. These assessments use lab-made antibodies to seek for antigens from the SARS-CoV-2 virus.
To run an antigen take a look at, you first deal with a pattern with a liquid containing salt and cleaning soap that breaks aside cells and different particles. You then apply this liquid to a take a look at strip that has antibodies particular to SARS-CoV-2 painted on it in a skinny line.
Identical to antibodies in your physique, those on the take a look at strip will bind to any antigen within the pattern. If the antibodies bind to coronavirus antigens, a coloured line seems on the take a look at strip indicating the presence of SARS-CoV-2.
Antigen assessments have various strengths. First, they’re really easy to make use of that individuals with no particular coaching can carry out them and interpret the outcomes – even at residence. In addition they produce outcomes shortly, sometimes in lower than quarter-hour. One other profit is that these assessments may be comparatively cheap at round $10-$15 per take a look at.
Antigen assessments do have some drawbacks. Relying on the state of affairs, they are often much less correct than PCR assessments. When an individual is symptomatic or has plenty of virus of their system, antigen assessments are very correct. Nonetheless, in contrast to molecular PCR assessments, antigen assessments don’t amplify the factor they’re searching for. This implies there must be sufficient viral antigen within the pattern for the antibodies on the take a look at strip to generate a sign. When an individual is within the early phases of an infection, not plenty of virus is within the nostril and throat, from which the samples are taken. So, antigen assessments can miss early instances of COVID-19. It’s additionally throughout this stage that an individual has no signs, so they’re extra more likely to be unaware they’re contaminated.
[Get the best of The Conversation, every weekend. Sign up for our weekly newsletter.]
Extra assessments, higher information
A number of antigen assessments are already obtainable over-the-counter, and on Oct. 4, 2021, the Meals and Drug Administration granted emergency use authorization to a different at-home antigen take a look at. The U.S. authorities can also be pushing to make these assessments extra obtainable to the general public.
At RADx, the challenge I’m part of, we’re presently conducting medical research to get a greater understanding of how antigen assessments carry out at numerous phases of an infection. The extra information scientists have on how accuracy modifications over time, the extra successfully these assessments can be utilized.
Understanding the strengths and limitations of each PCR and antigen assessments, and when to make use of them, can assist to deliver the COVID-19 pandemic beneath management. So the following time you get a COVID-19 take a look at, select the one that’s best for you.