At this point in the pandemic, I think it is safe to say that most people have done at least one COVID test. But have you ever found yourself wondering a bit more about the different diagnostics tests we use to screen for COVID-19? For instance, how do they work? What are their advantages and disadvantages? And when should each test be used? Such questions require a deeper dive into this topic, and fortunately your friends at BioDecoded have you covered.
COVID-19 tests can be divided into two main categories; one being molecular tests and the other being antigen tests. This week we will uncover the characteristics of molecular tests.
Molecular Tests
The first series of tests that were developed to detect COVID-19 were the molecular tests or nucleic acid* amplification tests (NAATs) [1]. The most used diagnostic method within this category is the well known polymerase chain reaction (PCR) test. These tests function by detecting the genetic material of the COVID-19 virus within a test sample, and then subsequently amplifying or producing multiple copies of it, to yield a positive signal. If a person is not infected by the virus, there is no genetic material to be amplified, thus no signal will be obtained, and the result will be negative. Samples from these tests are usually taken from swabs in the nose and throat, or from saliva samples [2,3]. These samples are then sent to a lab, processed, and results are obtained usually within one to seven days.
What are the advantages?
Detects small amounts of the virus (highest sensitivity).
PCR tests are considered the most accurate form of testing and considered to be the gold standard for detecting SARS-CoV-2.
Highly adaptable to an evolving virus.
Multiple samples can be processed at once.
If saliva samples are used, sampling is less invasive and easier.
What are the disadvantages?
Results aren’t obtained quickly.
Expensive.
Requires laboratory equipment.
Patients might still test positive for three or four weeks after infection.
When should these tests be used?
It is suggested that PCR tests be taken when one has been exposed to a known or probable COVID-19 case. It is also worth mentioning that the PCR method detects the virus before less sensitive antigen tests, therefore it is the preferred test for detecting an early COVID-19 infection. However, one must be weary after recovering from an infection, as according to Dr. Leana Wen, a CNN medical analyst, seven to ten days after post-COVID-19 recovery, a PCR test can still detect the virus’ genetic material [4].
If you want to learn about another type of COVID-19 test, known as antigen tests or rapid tests, stay tuned for next week’s post!
*Nucleic Acids - a type of molecule that contains genetic information in cells (see genetic code). The two types of nucleic acids are DNA and RNA.
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Written by: Renard
Edited by: María and Natasha
BioDecoded is a volunteer group committed to sharing accurate scientific information. For more information about vaccines and their safety profile, please see previous posts or consult with your personal physician. If you have any questions about this topic, please comment or send them to our email.
References:
Types of COVID-19 Tests, COVID-19 Testing Toolkit (2022). Available at: https://www.centerforhealthsecurity.org/covid-19TestingToolkit/testing-basics/types-of-COVID-19-tests/diagnostic-tests/molecular-tests.html#:~:text=Molecular%20tests%20amplify%20bits%20of,where%20virus%20might%20be%20found.(Accessed: 22 March 2022).
Which COVID-19 Test Should You Get? (2022). Available at: https://www.yalemedicine.org/news/which-covid-test-is-accurate (Accessed: 22 March 2022).
COVID-19 Test Basics (2022). Available at: https://www.fda.gov/consumers/consumer-updates/covid-19-test-basics(Accessed: 22 March 2022).
When you should take a PCR vs. a rapid antigen test, CNN (2022). Available at: https://edition.cnn.com/2022/01/19/health/pcr-vs-antigen-tests-covid-19-wellness/index.html(Accessed: 22 March 2022).https://biodecoded.net/glossary/
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