During a pandemic, the most crucial component to understanding and controlling the spread of a virus is by having accessible, accurate testing. For COVID-19, there are two common tests frequently performed to detect and confirm the presence of COVID-19: COVID-19 PCR tests and antigen tests. Both are administered in a similar way, but how they detect components of COVID differ.
What is the difference between PCR nasal swab and COVID-19 antigen test? Which is more accurate? Let’s explore each test, how they are administered, how they detect COVID-19, how long results take, and why each approach to COVID-19 testing is taken.
PCR is short for polymerase chain reaction. As the Mayo Clinic describes, the PCR COVID-19 molecular test detects genetic material of a virus within a fluid sample collected from the back of the nose.
How it’s administered
If you’ve had a COVID-19 test already, you’ve more than likely already had a PCR test conducted. A medical professional collects a sample from the nasopharyngeal floor—the very back of the nasal cana—by inserting a long swab through the nose of an upright patient. The swab will be rotated 2-3 times against the nasal floor to ensure enough sample material is collected to accurately detect the presence of SARS-CoV-2, the virus known to cause COVID-19. Once fluid material is collected, it’s inserted into a test tube and sent to a lab for diagnostic testing.
How it detects COVID
If present, the genetic components that make of COVID-19 are found within the collected saliva. The Cleveland Clinic details that a lab tech performs a process called extraction, which isolates genetic materials from the sample, including the SARS-CoV-2 virus. A PCR test then uses special chemicals and a polymerase chain reaction machine, called a thermal cycler, which will cause the SARS-CoV-2 genetic material to produce millions of copies. If COVID is present, the special chemicals used will produce a fluorescent light, which acts as a positive confirmation of COVID-19 present in the sample. The patient is then informed of the positive, or negative, test results.
How long does it take to run a PCR covid test?
If the test is performed immediately on-site, it can be possible to understand the results within minutes. However, PCR testing requires special equipment and conditions which typically means that test samples need to be sent to testing laboratories. Then, the timing is dependent on a series of factors, like staffing resources, length of testing queue, and more. The standard window for results is 1-3 days.
Why it’s used
There are less false positives and negatives associated with PCR COVID tests, meaning more individuals and organizations choose this test for more accurate and reliable results. The longer wait time is worth knowing that the results are accurate. Because of this, most organizations and businesses that collect test results from employees will require PCR tests.
Also known as the ‘rapid test,’ many people looking for quick answers will take the antigen test, meaning they can receive results within minutes.
is administered through a nasopharyngeal swab test, the same as with the PCR test. The antigen then searches for traces of antigens, or proteins found on the surface of a virus.
How it’s administered
Patients taking an antigen test will experience an identical administration as with the PCR test. A medical professional will insert a long swab into the nose until it reaches the back of the nasal cavity, called the nasopharyngeal floor, where a fluid sample is collected. The sample is then directly inserted into a testing reagent.
How it detects COVID
When the body is infected with a virus, it will detect and analyze proteins found on the surface of the virus, called antigens. The body then creates its own proteins specifically designed to fight against the virus. These are called antibodies. The rapid antigen test searches for traces of those antigens within the collected sample.
Antigen proteins can sometimes be present and detectable within a sample, even if there is not enough to be cultured. Because of this, antigen tests can provide a higher rate of producing false positives, meaning they have found the virus is present even if there is not enough of it to survive and develop into COVID-19.
How long does it take to get results for COVID19 antigen tests?
Known for its rapid results window, antigen tests can take as little as 15 minutes to produce a result.
Why it’s used
Antigens are most prominent within the first few days of infection, which makes antigen tests most accurate if taken early on as symptoms arise. Due to the ability to produce rapid results, the antigen test is best taken within a few days after symptoms arise. Because there is a higher failure rate, most individuals will use the antigen test to quickly confirm symptoms prior to additional testing. It’s recommended that individuals also take a PCR test even if an antigen test produces a negative result.
So, what is the difference between PCR nasal swab and COVID19 antigen test? Aside from a very similar sample collection process through nasal swabs, the science behind the tests are different in that they are searching for different components. While antigen tests can provide quicker results, they can have a higher rate of false positives and negatives, which means that they may miss an active infection and produce an inaccurate positive or even detect the presence of COVID even if it’s not there.
The types of tests have different purposes. COVID-19 PCR and antigen tests seek to detect the presence of COVID-19 material within a fluid sample collected from the nasal cavity. The antibody blood test searches for the presence of virus-fighting proteins called antibodies, which become present after infection or vaccination and suggest a level of immunity.