With Christmas across the nook and COVID-19 case numbers rising, it’s necessary to maintain getting examined when you may have signs, have been uncovered to the virus, or are going to a high-risk atmosphere.
Now we have now entry to PCR exams (often known as RT-PCR, or reverse transcription-polymerase chain response, exams) and fast antigen exams to detect SARS-CoV-2, the virus that causes COVID.
So which take a look at must you use? And what’s the distinction?
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How the exams work
In Australia, PCR exams are used to diagnose SARS-CoV-2 infections. This take a look at seems for SARS-CoV-2 genetic materials.
RT-PCR converts viral RNA to DNA and amplifies the genetic sequence, making billions of copies, to some extent the place these copies may be detected.
As a result of the take a look at can amplify tiny quantities of viral genetic materials, it’s thought of the gold customary and may detect an infection in earlier phases than different exams like fast antigen exams.
Speedy antigen exams as a substitute detect viral proteins. The proteins bind within the resolution to antibodies that turn into fluorescent to point the presence of the proteins.
Speedy antigen exams are:
faster than PCR exams (15-20 minutes versus hours to days to get a outcome)
may be executed within the house in comparison with having to line up and look forward to a swab, which then must be analysed in a laboratory.
However they’re much less delicate than a PCR take a look at as a result of there isn’t any amplification course of.
How efficient are they?
Whereas each exams usually tend to appropriately detect an an infection when the particular person’s viral load is excessive, PCR exams are extra delicate than fast antigen exams.
An Australian research evaluating the sensitivity (appropriately diagnosing SARS-CoV-2 an infection when you may have it) of 1 sort of fast antigen take a look at in comparison with a PCR take a look at, discovered 77% of constructive antigen take a look at outcomes aligned with PCR take a look at outcomes.
This rose to 100% when folks have been examined inside per week of the onset of signs.
Speedy antigen testing is not excellent. However it could possibly be a helpful a part of Australia’s COVID response
The Therapeutic Items Administration offers an inventory of accredited fast antigen exams, which have outcomes that align with PCR take a look at 80-95% of the time, offered the take a look at is completed inside per week of symptom onset. A few of these exams are rated as very excessive sensitivity, with 95% settlement with PCR exams.
Which take a look at to take when?
Take a RT-PCR take a look at in case you:
have COVID signs
have a identified publicity to somebody with COVID
do a fast antigen take a look at and get a constructive outcome, as a result of PCR affirmation is required
are required to by your well being division to be launched from quarantine or isolation
are required to by a well being division to get permission to journey to a location.
A PCR is the take a look at of selection in these conditions as a result of it’s extra correct at diagnosing an an infection.
Take into account a fast antigen take a look at in case you:
are planning to go to a delicate web site (for instance, an aged care facility)
are planning to have contact with somebody at excessive danger from COVID (for instance, an aged particular person or somebody on immunosuppressive remedy), and also you need to defend them
have COVID signs however can’t get to a PCR testing web site
are going to an occasion the place a number of folks might be mixing, significantly if it’s being held indoors the place the danger of transmission is significantly larger
need to rapidly verify whether or not you might need a SARS-CoV-2 an infection
are a part of an everyday COVID surveillance program (some workplaces require it, significantly in conditions the place the particular person will not be absolutely vaccinated).
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The fast antigen take a look at is taken into account to be a screening instrument. In different phrases, it could point out that you just is perhaps contaminated, however a PCR take a look at is required to substantiate the outcome.
Whereas a detrimental fast antigen take a look at outcome will not be a assure that you just aren’t contaminated, it does present extra safety on your contacts than not testing.
How usually ought to I take a fast antigen take a look at?
It relies on the explanation you take the take a look at. When you’re a part of a surveillance program, take the take a look at if you end up requested to.
When you don’t have signs, taking the take a look at two to a few instances over per week may also help enhance take a look at sensitivity as a result of viral load waxes and wanes. Check sensitivity might be highest when the viral load is at its peak.
How does the Omicron variant have an effect on testing?
The extremely mutated Omicron variant seems to nonetheless be detected by each PCR and fast antigen exams.
Ordinarily, a PCR take a look at signifies whether or not or not you may have a SARS-COV-2 an infection however not which variant you may have. Genome sequencing is required to seek out that out.
Nevertheless, some PCR exams search for a particular genetic sequence that’s lacking within the Omicron variant (known as S gene goal failure). These specific PCR exams can’t solely detect a constructive outcome but in addition whether or not it’s more likely to be the Omicron variant.
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Thea van de Mortel teaches into the graduate An infection Prevention and Management program at Griffith College.