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Breaking Down COVID-19 Testing: When and How to Test

Thursday, January 27, 2022 10:26 AM

By: Angelina Campanile

A high demand for COVID-19 testing has made at-home tests an essential item in our medicine cabinets.

Although at-home tests can present results in less than 20 minutes, they can issue false negatives if done incorrectly.

Here, Paige Larkin, PhD, Director of NorthShore’s Molecular Microbiology Lab, explains what you need to know about the different types of COVID-19 tests, when to test, how to test, and what to do when you receive your results. 

What are the different types of COVID tests?

There are two main types of tests to detect COVID-19:

  1. PCR – Polymerase chain reaction (PCR) tests detect the RNA of the virus. They are performed in a laboratory and can take a few days to administer results.

  2. ANTIGEN – Antigen tests, more commonly known as “rapid” tests or at-home tests, detect the proteins of the virus. You can buy these tests online or at the pharmacy, and retrieve results within 20 minutes.

COVID testing infographic

Which is more accurate: Rapid at-home tests or PCRs? 

PCR tests are more sensitive than at-home tests and better at picking up infections earlier. The at-home test is able to detect the virus only when the viral load is very high.

Receiving a negative result after taking an at-home test does not ensure you are COVID free. It’s possible the amount of virus in your system didn’t meet the test’s threshold, you may have tested too soon, or you may have incorrectly conducted the test.

Positive means positive. But the best way to ensure that you are COVID negative is to re-test a few days later or confirm with a PCR test. Even after testing negative with a rapid test at home, you can still test positive on a PCR.

Remember: Testing is just a snapshot in a moment of time. Although you may test negative today, that doesn’t mean you’ll be negative tomorrow.

When should I test?

Symptomatic
The most common COVID-19 symptoms include nasal congestion, runny nose, sore throat, fatigue, body aches, headaches, and/or other symptoms you may have upon contracting the common cold or the flu.

Even if you’re fully vaccinated and boosted, you can still show symptoms, and you can still be contagious.

Here’s a rule of thumb: if you’re symptomatic or have known exposure, TEST. 

Asymptomatic
Everyone can react differently to COVID-19, and the omicron variant demonstrates that you can still test positive and shed virus even if you’re asymptomatic.

Case 1: I’ve been exposed but I’m fully vaccinated, boosted and I’m not showing any symptoms.
CDC: You do not need to quarantine, but you should test on Day 4, 5 or 6 following exposure. 

Case 2: I’ve been exposed and I’m fully vaccinated but I’m not boosted and I’m not showing any symptoms. 
CDC: Quarantine for five days following exposure and wear a mask around others for five days after that. Test on Day 4, 5 or 6. Testing too soon can give a false negative result.

Case 3: I’ve been exposed, I’m not vaccinated or boosted, but I’m not showing any symptoms. 
CDC: (Same as Case 2) Quarantine for five days after exposure and wear a mask around others another five days after that. Test on Day 4, 5 or 6. 

If you take a rapid at-home test on Day 1, 2, or 3 following exposure, the test can be a false negative. The tests are most accurate when you are the most contagious, which the CDC says can be Days 4, 5 or 6 whether or not you’re symptomatic.

For the latest CDC guidelines, click here.

How do I take an at-home test?

Instructions for at-home COVID-19 tests can vary, so it’s crucial to read and follow the instructions verbatim. Getting creative or trying to complete the test from memory could result in user error and an inaccurate result.