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Last updated May 14, 2021. 8 minute read

How does a mouth swab COVID-19 test work?

You may have seen claims circulating that mouth swab tests are less reliable than nasal swabs. But the story is a little more complicated than that. We’ve covered everything you need to know about mouth swab COVID tests, how they work, how reliable they are and when to get one.

Linnea Zielinski Written by Linnea Zielinski
Reviewed by Yael Cooperman, MD

Getting tested for coronavirus disease 2019 (COVID-19) can be overwhelming, even if you’ve already had one test or many. But this far into the pandemic, testing should be something that alleviates stress—not something that causes it. 

Still, there is so much ever-evolving information about COVID-19 testing that it can feel like you need to be a medical professional to even know where to turn first. If you’re trying to figure out whether to get tested and how, we’re here to help. Here’s what you need to know about mouth swab COVID tests, and other options for finding out if you have COVID-19.

Vitals

  • To find out if you have COVID-19, there are a few tests you can take including mouth swabs, nose swabs, and others that require you to spit into a test tube. 
  • During a mouth swab test, a cotton swab is used to collect a sample from inside your mouth. This is different from a saliva test, which requires you to spit into a small container.
  • Different testing sites have different testing methods.

What types of COVID-19 tests are there?

When it comes to diagnosing COVID-19, there are two main types of tests usually performed: 

  • Molecular tests, like polymerase chain reaction (PCR) tests, which look for the virus’s genetic material
  • Antigen tests, which look for the virus’s outer shell

Both of these tests are done using nose or mouth swabs. PCR tests can also be done using saliva (FDA, 2020-a). The saliva and mouth swab tests sound like the same thing, but they’re not. What’s the difference? A saliva test requires you to spit into a tube, while a mouth swab test involves rubbing the inside of your mouth with a cotton swab to get a sample. 

Nasal swabs follow the same protocol, except you or a healthcare professional takes a swab sample from your nose instead of your mouth.

You may have also heard of antibody tests. These tests look for antibodies, which are the body’s response when invaders—like the coronavirus—are present in your system. 

Antibody tests are typically done using a blood sample, and unlike antigen tests, can’t tell you if you currently have COVID-19. Instead, these tests see if your immune system has reacted to a COVID-19 infection in the past. An antibody test can also show if you’ve been vaccinated.

Which COVID-19 test is most reliable?

What type of COVID-19 test you get usually depends on where you live, and what’s available.

You may have seen claims circulating that mouth swab tests are less reliable than nasal swabs. But how is that measured? No matter the type, the accuracy of all COVID-19 tests are described in terms of sensitivity and specificity, which refers to how accurately the tests identify the virus in your system (Swift, 2020). For example, a test that has 97% sensitivity can accurately identify 97 out of 100 COVID-19 cases. However, in the other three cases, it will give false negatives, meaning it says you don’t have COVID-19 even though you do.

Molecular tests like PCR are generally considered to be the most accurate COVID-19 tests, but even these have limitations and are typically less accurate in real life than in laboratory settings (Yohe, n.d.). In addition, PCR tests take longer than rapid antigen tests and require special machinery, meaning they’re not always the best option.

Antigen tests might not be quite as good at identifying every case of COVID-19, but tests that come back positive are considered extremely accurate. You may need a PCR test if your antigen test comes back negative, though, especially if you have a known exposure to a person who tested positive or if you have symptoms of COVID-19 (FDA, 2020-a). Different antigen tests have different accuracy, but one test studied can accurately identify 80 out of 100 cases of COVID-19 when people have symptoms and 40 out of 100 cases when people are asymptomatic (Pray, 2020).

Why do some tests have false negatives?

Sometimes tests aren’t accurate. If a person has COVID-19, but the test says they don’t, that’s called a false negative. 

A false negative can happen with any type of test but is typically more common if you only have a small amount of the virus in your body. This can happen early on in the infection—often before a person even develops symptoms. It can take between two and 14 days to develop symptoms of COVID-19 from the time you were exposed (CDC, 2021). Early on in the infection, you might have very little virus in your body and the test can miss it. 

What happens after I get my test results?

Even if your COVID-19 test comes back negative, it doesn’t mean it’s time to visit your grandparents. 

Not only can results be inaccurate in some cases, but COVID-19 tests are also just a snapshot of the overall picture. You could have the virus, just not enough in your system yet to appear on a test. Even if you tested negative before, you could still catch COVID-19 at the gas station or any other stop on the way to visit family or friends. This is why it’s important to practice social distancing, avoid going out without a mask covering your nose and mouth, and avoid spending time with people who aren’t part of your household until you are fully vaccinated (CDC, 2020-b). 

Remember: a COVID-19 test result isn’t the final word, even if you are already vaccinated. If you have symptoms of COVID-19 and your test is negative, consult with a healthcare provider about getting another test and consider isolating yourself from the other people in your home (CDC, 2020-b). Your healthcare provider will take into account your symptoms and any exposures you might have had when deciding whether or not to send you for another test. 

Not every COVID-19 case requires an in-person evaluation by a healthcare professional. Studies have found that between 20 and 31% of people with COVID-19 will be asymptomatic the entire time they’re sick (Buitrago-Garcia, 2020). According to the World Health Organization, 80% of people with confirmed cases of COVID-19 have mild-to-moderate symptoms (WHO, 2020). If your symptoms remain mild, you may be asked to remain home and isolate rather than leave the house to get tested and potentially expose other people to COVID-19. 

Before you start visiting with people outside of your household it’s important to make sure that you’re fully vaccinated. Now that the vaccines are so widely available, it’s a lot easier to get your shots. Once you’re fully vaccinated, you can even visit with other vaccinated people, according to the CDC.

How to do a mouth swab COVID-19 test

There are different ways the mouth swab COVID-19 test may be done:

  • A healthcare professional may swab your mouth for you.
  • A healthcare profession may supervise while you do it yourself.
  • You may be given a kit at a testing location with instructions for how to swab your own mouth.
  • You can use an at-home mouth swab kit.

You may need to take certain steps before the test to make sure the results are as accurate as possible. If you need to book an appointment, ask if there’s anything you should avoid on the day of your test. Some types of tests that use saliva require that you don’t eat, drink, smoke, brush your teeth, or chew gum 30 minutes before the test (FDA, 2020).

You may be reminded to cough forcefully 3-5 times and keep the phlegm in your mouth before you swab if a medical professional is conducting or supervising the test. That’s because coughing brings up secretions from your lungs, and preliminary research suggests this improves the chance of identifying coronavirus in samples (Kojima, 2020).

If someone is administering the test, they will swab the inside of your mouth. If it’s a self-collection test, you’ll have a sheet with instructions outlining the process.

Where to get a mouth swab COVID-19 test

If you’re currently experiencing symptoms of COVID-19, if you’ve been in close contact (within six feet for 15 minutes or more) with someone with a confirmed case of COVID-19, or if your healthcare provider tells you to do so, you should go get tested. People who have taken part in any activity that puts them at a higher risk for COVID-19 because they cannot socially distance themselves should also get a test done. That includes travel, large get-togethers, or crowded indoor settings (CDC, 2020-d).

If you’re unsure whether you need to get tested, you can use the CDC’s self-checker tool (CDC, 2020-e).

If you know you’ve been in close contact with someone with COVID-19 or in a situation that puts you at risk of getting it, you can speak with your healthcare provider, your local urgent care, or your state or local health department to find out where to get tested (CDC, 2020-a).

The U.S. Food and Drug Administration (FDA) has granted emergency use approval for some at-home molecular and antigen tests that don’t require a prescription and can be ordered online, but both of them are nasal swab tests (FDA, 2020-b; FDA, 2020-c). The molecular tests need to be sent back to the lab for analysis.

Some pharmacies may be offering access to COVID-19 tests, but most offer nose swab tests instead of mouth swabs. These tests are just as quick as mouth swab tests. While they can be a little bit uncomfortable, they’re not painful. CVS’s MinuteClinic has a tool for finding a participating location in your area (CVS, n.d.). Rite Aid and Walgreens offer similar services (Rite Aid, n.d., Walgreens, n.d.). Quest Diagnostics also offers testing at select Walmart locations (Quest Diagnostics, n.d.).

References

  1. Buitrago-Garcia, D., Egli-Gany, D., Counotte, M. J., Hossmann, S., Imeri, H., Ipekci, A. M., . . . Low, N. (2020). Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis. PLOS Medicine, 17(9). doi:10.1371/journal.pmed.1003346. Retrieved from https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1003346
  2. Centers for Disease Control and Prevention (CDC). (2020-a, August 06). State and Territorial Health Departments – STLT Gateway. Retrieved January 08, 2021, from https://www.cdc.gov/publichealthgateway/healthdirectories/healthdepartments.html
  3. Centers for Disease Control and Prevention (CDC). (2020-b, October 21). Test for Current Infection. Retrieved January 08, 2021, from https://www.cdc.gov/coronavirus/2019-ncov/testing/diagnostic-testing.html
  4. Centers for Disease Control and Prevention (CDC). (2020-c, December 1). Fact Sheet for Patients: CDC 2019-nCoV Real-Time RT-PCR Diagnostic Panel. Retrieved January 08, 2021, from https://www.cdc.gov/coronavirus/2019-ncov/downloads/Factsheet-for-Patients-2019-nCoV.pdf
  5. Centers for Disease Control and Prevention (CDC). (2020-d, December 7). Testing for COVID-19. Retrieved January 08, 2021, from https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/testing.html
  6. Centers for Disease Control and Prevention (CDC). (2020-e, December 28). Coronavirus Self-Checker. Retrieved January 08, 2021, from https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/coronavirus-self-checker.html
  7. Centers for Disease Control and Prevention (CDC). (2021, January 7). Clinical Questions about COVID-19: Questions and Answers. Retrieved January 09, 2021, from https://www.cdc.gov/coronavirus/2019-ncov/hcp/faq.html
  8. CVS. (n.d.). COVID-19 Testing and Locations. Retrieved January 09, 2021, from https://www.cvs.com/minuteclinic/covid-19-testing?icid=poct-covid19-mc-cliniclocator
  9. Food and Drug Administration (FDA). (2020-a, November 6). Coronavirus Disease 2019 Testing Basics. Retrieved January 12, 2021, from https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics
  10. Food and Drug Administration (FDA). (2020-b, December 9). Coronavirus (COVID-19) Update: FDA Authorizes First Direct-to-Consumer COVID-19 Test System. Retrieved January 09, 2021, from https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-first-direct-consumer-covid-19-test-system
  11. Food and Drug Administration (FDA). (2020-c, December 15). Coronavirus (COVID-19) Update: FDA Authorizes Antigen Test as First Over-the-Counter Fully At-Home Diagnostic Test for COVID-19. Retrieved January 09, 2021, from https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-antigen-test-first-over-counter-fully-home-diagnostic
  12. Kojima, N., Turner, F., Slepnev, V., Bacelar, A., Deming, L., Kodeboyina, S., & Klausner, J. (2020). Self-Collected Oral Fluid and Nasal Swabs Demonstrate Comparable Sensitivity to Clinician Collected Nasopharyngeal Swabs for Covid-19 Detection. doi:10.1101/2020.04.11.20062372. Retrieved from https://www.medrxiv.org/content/10.1101/2020.04.11.20062372v1.full-text
  13. Pray IW, Ford L, Cole D, et al. Performance of an Antigen-Based Test for Asymptomatic and Symptomatic SARS-CoV-2 Testing at Two University Campuses — Wisconsin, September–October 2020. MMWR Morb Mortal Wkly Rep 2021;69:1642–1647. DOI: 10.15585/mmwr.mm695152a3. Retrieved from https://www.cdc.gov/mmwr/volumes/69/wr/mm695152a3.htm
  14. Quest Diagnostics. (n.d.). Drive up. Get Tested. Retrieved January 12, 2021, from http://patient.questdiagnostics.com/myquestcovidtest
  15. Rite Aid. (n.d.). Free Drive-Thru COVID-19 Testing. Retrieved January 12, 2021, from https://www.riteaid.com/pharmacy/services/covid-19-testing
  16. Swift A, Heale R, Twycross A. What are sensitivity and specificity?. Evid Based Nurs. 2020;23(1):2-4. doi:10.1136/ebnurs-2019-103225. Retrieved from https://pubmed.ncbi.nlm.nih.gov/31719126/
  17. Walgreens. (n.d.). COVID-19 Testing & Locations: Walgreens Find Care. Retrieved January 12, 2021, from https://www.walgreens.com/findcare/covid19/testing?group=b&
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