COVID-19 test: what you need to know

January 14, 2022 4:00 p.m.

Author:
University of Utah Health Communications

There are two types of tests, PCR and antigen.

A PCR test detects viral RNA. This is the type of test you need to take at a test center, where testers will use either a nasal swab or your saliva for the test. Turnaround time will vary depending on testing capabilities in your area, but during a surge in cases, it may take 24 hours to several days to get results.

Antigen tests (rapid tests) detect proteins on the surface of the virus. These tests are available at test centers and in over-the-counter kits. The results of these tests can come back in as little as 15 minutes.

Both of these tests can be useful, but it can be difficult to know which is best for your particular situation.

Emilie Spivak, MD, MHS, associate professor of infectious diseases at the University of Utah Health, offers the following information on how to test, when to test, and which test is best.

If you think you have COVID-19, should you take a PCR test or a (rapid) antigen test?

Ideally a PCR, as it is more sensitive and accurate and more likely to detect the COVID-19 virus. In fact, the demand for this type of test is huge right now due to the surge of Omicron, and it can take days to get a result. If this is the case in your area, a rapid home test kit is useful given its good performance during the symptomatic phase of illness, especially after 12-24 hours of symptoms.

If you have been exposed to COVID-19, what day should you get tested?

The recommendation is three to five days after exposure. If you are symptomatic, sooner. If you have had a high-risk exposure and a rapid test is negative, it is best to follow up with a PCR test to truly rule out COVID-19 infection.

With testing shortages and long lines, can you skip testing and just assume you have the virus if you have symptoms?

It’s always best to get tested, especially if you’re at high risk for serious illness, work in healthcare, or interact with vulnerable populations. But if COVID-19 rates are high in your area, it’s reasonable to assume you have it if you’re showing symptoms. I would add that if you are sick, even if you don’t have COVID-19, staying home is a good idea. Our healthcare systems are overwhelmed at the moment, whether it’s COVID-19, the flu or other infectious diseases, please isolate yourself if possible and always wear a quality mask if you need to go out in public. .

Are over-the-counter rapid tests as accurate at detecting COVID-19 as other methods?

Rapid tests are less sensitive than PCR tests, but they have a sensitivity rate of around 90% when people are symptomatic. They are less sensitive in asymptomatic people. And if you use a rapid test too soon, fewer viruses may be present, leading to a negative result. Again, if you test early with symptoms and the result is negative but you think you have COVID-19, repeat the test 24-48 hours later or continue the PCR test.

Some people share on social media that you should swab your throat instead of your nose if you’re using a home test kit. Is it recommended?

Some unpublished data suggest that early in infection, sore throat is a common symptom. And viral replication with Omicron can start at high levels in the throat and later ascend to the nasal passages. This can make nasal tests negative at the onset of symptoms. At this time, I would recommend people try to continue saliva PCR testing as soon as symptoms appear or use a repeat rapid antigen testing strategy.

People anecdotally share that you may get a better result by scrubbing the throat, or scrubbing the throat first and then scrubbing the nostrils, but this is not currently recommended by the test manufacturers. The information is still emerging, and we need to study it before we can recommend it.

Are rapid tests less accurate in detecting the Omicron virus?

We do not know yet. Studies are yet to come, but from what we know so far, rapid tests are still effective at detecting Omicron. However, they may be less accurate on the first day of symptoms, so assume you have COVID-19 and wait to test on the second day of symptoms, or repeat the test if initially negative.

How accurate are PCR tests? Some people who test negative for PCR are still convinced they have COVID-19. What advice do you have for people who test negative but show symptoms of illness?

PCR tests are very accurate, but they are not 100% accurate, and they are also subject to the accuracy of the sample taken. If you test negative but have symptoms of COVID-19 illness, isolate yourself at home if you can and try to repeat the test within 24 hours. Also be aware that other respiratory viruses are circulating in the community and it is important to stay home to stop the transmission of other viruses as well.

What should people who need a test result do before they can have another procedure such as surgery or monoclonal antibodies?

A PCR test is best, but if you need a result quickly, you may not be able to get one depending on the backups in your area. If so, I would recommend a quick test, but you’ll also need to check the requirements for your particular procedure. Talk to your healthcare provider about your best option.

If you have had COVID-19 and no longer have symptoms, and it has been five days since your symptoms first appeared, do you need to be tested again? Or can you safely return to work with a quality mask?

Talk to your employer about the requirements of your workplace. Current CDC guidelines recommend that if you can test, do so, but it is not required. If you have no symptoms, you can return to work, but you must wear a quality mask, such as a KN95, for at least another five days. If after five days you still have a fever or a severe cough, do not come out of isolation until your symptoms disappear. It’s important to note that a cough can persist for days or weeks, so use discretion if your cough is productive and frequent. But if it’s a dry, intermittent cough and your other symptoms have gone away, you’re probably safe to get out of isolation, as long as you can keep wearing a mask.

My main advice right now is to vaccinate, get your booster, use a high quality mask such as a KN95, practice social distancing, work from home if you can, and test if you think have the virus. If you cannot test but feel ill, please self-isolate if you can. Many people describe this virus as less severe than other variants, but it is no less severe for our healthcare systems, and we are seeing incredibly sick people in our hospitals. Do not assume that you will only have minor symptoms if you receive Omicron.