How Does COVID-19 Testing Work?

by Victor Fang

The Importance of Testing

Laboratory and at-home testing are essential in the fight against COVID-19. Symptoms of infection vary, ranging from mild flu-like symptoms to severe illness such as confusion or difficulty breathing. A significant percentage of people (about 17%) who are infected by COVID-19 don’t show any symptoms at all—and asymptomatic carriers are still capable of transmitting the virus to others! Testing for COVID-19 allows for an accurate and timely diagnosis of infection regardless of symptoms, which enables proper social isolation and early treatment.

Types of Testing

The two main categories of tests are diagnostic tests and serology tests. Diagnostic tests are used to determine if someone is currently infected by COVID-19, and serology tests are used to check if someone has previously been infected. Serology tests are not frequently used to diagnose COVID-19, rather they have applications in epidemiology and public health for analyzing how the virus is spreading in the community.

Diagnostic Tests

The most common diagnostic test is PCR testing, better known as the nasal swab test, in which a sample is collected from the upper respiratory tract, and then analyzed in a lab for viral nucleic acid. To do this, the sample is incubated in a lab with reagents such as reverse transcriptase and DNA polymerase. These enzymes use the SARS-CoV-2 mRNA as a template to create DNA, which can then be duplicated to make millions of copies of the virus’ genetic instructions. This technique called reverse transcriptase-polymerase chain reaction (RT-PCR) is used to greatly amplify the amount of genetic material present, making it much easier to detect even trace amounts of COVID-19.

The time it takes to produce any results may range from minutes up to a few days depending on lab availability, but this method has shown to be very accurate and is definitely worthwhile. That being said, a positive or negative result is not definitive. False negatives often occur when patients have non-viable or inactivated viral material in their nose/throat. When PCR tests return positive, it indicates the presence of viral DNA/RNA. However, it doesn’t tell us how much viral material there is, if the virus is currently replicating, or if the patient is infectious. Still, PCR testing plays a huge role in letting patients know if they’ve been exposed to COVID-19.

Lateral Flow Tests

Another common form of diagnostic testing is the lateral flow antigen test, also known as rapid home testing or immunochromatographic assays. To use a lateral flow test, a nasal sample is placed on a small pad at one end and flows to the other end through capillary action. If any viral particles are present, they will attach to a line of labeled antibodies, bringing them along to the test line where they then attach to another line of antibodies. A positive result would appear as a visible colored line due to these labeled antibodies. If the SARS-CoV-2 virus isn’t present in the sample, the labeled antibodies flow along with the sample, but continue past the test line and end up on the other side of the pad. There would not be a visible colored line present at the test line. The benefits of home testing over lab tests includes its accessibility, convenience, and quick results. However, at-home testing can be misleading because it provides less accurate results, and the test may be carried out or interpreted incorrect

Serology Testing

Serology tests (antibody tests) check an individual’s blood serum for antibodies that may have been produced in response to COVID-19. This type of testing is not frequently used to diagnose an active infection as it may take many days for the immune system to generate antibodies. Instead, they are mainly used to collect data on who has been infected and how COVID-19 is spreading throughout the community.

Who Should Get Tested?

According to the FDA, you should get tested for COVID-19:

• If you have symptoms of COVID-19, even after vaccination

• If you have had close contact (within 6 feet for a total of 15 minutes or more) with someone with confirmed COVID-19, even after vaccination

• If you took part in activities that put you at higher risk for COVID-19 because you could not socially distance as needed, such as travel, attending large social or mass gatherings, or being in crowded indoor settings

• If you have been asked or referred to get tested by your healthcare provider, or local or state health department

If your test turns out positive, you are advised to stay at home and socially isolate yourself from others. Regardless of your result, everyone is encouraged to help stop the spread of COVID-19 by practicing proper safety measures including social distancing, wearing masks, and maintaining proper hygiene.

References

1. https://www.publichealthontario.ca/en/diseases-and-conditions/infectious-diseases/respiratory-diseases/novel-coronavirus/lab-testing-ontario

2. https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics

3. https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/symptoms.html

4. https://www.nature.com/articles/d41586-020-03141-3#:~:text=The%20analysis%20defined%20asymptomatic%20people,for%20at%20least%20seven%20days.

5. https://www.nia.nih.gov/news/why-covid-19-testing-key-getting-back-normal

6. https://www.genome.gov/about-genomics/fact-sheets/Polymerase-Chain-Reaction-Fact-Sheet

7. https://www.fda.gov/media/136151/download

8. https://www.medicaldevice-network.com/features/types-of-covid-19-test-antibody-pcr-antigen/

9. https://www.creative-diagnostics.com/Immunochromatography-guide.htm