What is the difference between PCR testing and antigen screening? When should I do which test?
What is the detection principle
At present, PCR diagnosis of new coronavirus infection is to find the genetic material of new coronavirus through testing.
The reverse transcriptase-polymerase chain reaction reverse-transcribes viral RNA into DNA and amplifies the gene sequence, making billions of copies to detectable quantities.
Because this test can amplify tiny amounts of viral genetic material, it is considered the gold standard and can detect viral infection earlier than other tests such as rapid antigen testing.
In contrast, rapid antigen tests can detect viral proteins. The protein binds to the antibody in solution, and the antibody fluoresces, indicating the presence of the protein.
Rapid Antigen Test:
Faster than PCR (Polymerase Chain Reaction) testing (no need to wait hours or even days for results in 15-20 minutes)
It can be done at home without having to wait in line for a swab test, which is then sent to a lab for analysis.
However, it is not as sensitive as PCR (polymerase chain reaction) detection because it has not undergone gene sequence amplification.
How effective is it?
Both tests are more accurate at detecting viral infection when the person's viral load is high, but PCR (polymerase chain reaction) tests are more sensitive than rapid antigen tests.
A study that compared the sensitivity of the two tests (correctly diagnosing the virus in patients with COVID-19) found that one type of rapid antigen test had 77 percent of positive antigen test results compared to PCR (polymerase chain reaction) test results. Consistent.
That rose to 100 percent when tested within a week of symptoms onset.
The Australian Therapeutic Goods Administration (TGA) has a list of approved rapid antigen tests that subjects tested within a week of symptom onset and whose results were consistent with PCR testing 80-95 percent of the time. Some of these tests are rated as extremely sensitive, with 95 percent concordance with PCR tests.
Which test should be done? When do you do it?
RT-PCR (reverse transcriptase-polymerase chain reaction) testing is required if:
have symptoms of COVID-19
Known exposure to someone with COVID-19
Rapid antigen test results are positive and need to be confirmed by PCR
Health authorities require testing before release from quarantine
Health authorities require testing before getting permission to travel to a place
Consider getting a rapid antigen test if you:
Plan to visit a high risk setting (such as an aged care facility)
May come into contact with people at high risk of infection (such as the elderly, or people who are receiving immunosuppressive therapy) and you want to protect them
Symptoms of COVID-19, but unable to go to the PCR testing site
Participate in events with a larger number of people onsite, and the risk of infection is much higher if it is an indoor event
Want to quickly test yourself for SARS-CoV-2
Participate in a regular COVID surveillance program (required by some workplaces, especially those in industries that expose people who are not fully vaccinated)
Rapid antigen tests are often used as a screening tool and can detect that you may have COVID-19, but PCR monitoring is required to confirm the final result.
While a negative rapid antigen test result doesn't necessarily mean you don't have the infection, it at least protects your contacts better than no testing at all.
