Many of us are hearing stories lately about friends, neighbors and family members testing positive for the COVID-19 virus, even though official case numbers are likely being undercounted.
Health officials confirm that North Carolina is experiencing a COVID surge right now, and testing is an important tool in slowing the spread of the virus.
If you’re experiencing COVID symptoms and an at-home rapid test shows a negative result, does that mean you’re in the clear? Should you do follow-up testing to be sure?
We’ve heard from readers who have gotten negative results from their at-home rapid test only to get a positive result with a PCR test the next day, so we reached out to UNC Health to understand why at-home tests might give false-negative results — and to get tips on what to do if this happens to you.
Here’s what we learned from Dr. Melissa Miller, a professor in the UNC School of Medicine’s Department of Pathology and Laboratory Medicine.
Why might an at-home test not detect COVID?
Whether a COVID test returns positive or negative results depends largely on two factors, Miller said: the sensitivity level of the test and the viral burden of the disease in your body when you take a test.
If you’re experiencing COVID symptoms or have been exposed to the virus, at-home rapid tests are a relatively easy and convenient way to determine whether you have the virus — but it’s worth noting that they are less sensitive and have a higher risk for false negative results than lab-based PCR tests, such as those you might be tested with at a COVID testing site or in a health care setting.
That means, in relation to how long you’ve been experiencing symptoms or how long it’s been since you were exposed to the virus, PCR tests will return positive results for COVID before an at-home test does.
When a test detects the virus is largely dependent on the level of “viral burden” — how much virus you have in your body — at a given point during the disease’s course in your body.
A PCR test, being more sensitive, is more likely to detect the virus earlier, when your body’s viral burden is at a lower level, compared to an at-home test, which likely will not detect the virus until later, when the viral burden reaches its peak, Miller said.
Thinking about viral burden, it’s important to think about the time elapsed from when you were exposed to the virus to when you began having symptoms. Those timelines are different for different variants of COVID, and could affect when you receive a positive or negative test result, depending on which kind of test you take.
Miller gave the following examples of symptom onset timelines for different variants of the COVID virus and how they relate to viral burden:
▪ With the delta variant and other variants before omicron, it generally took about five to seven days for someone who was exposed to COVID to begin experiencing symptoms.
▪ With the omicron variant, which is currently the predominant variant in the U.S., people generally start to experience symptoms within three days of being exposed to the virus.
▪ With the shorter timeline from exposure to the onset of symptoms for the omicron variant, “there is less time for the virus to get to its highest load when first testing,” Miller said, “which can lead to false negative results in a less sensitive test,” such as an at-home, rapid test.
In other words, for previous variants of the virus, it took longer for people to develop symptoms, allowing higher levels of the virus to build in the body before people noticed they were sick. By the time people developed symptoms of those variants, generally after five to seven days of the virus being in their body, the levels of the virus were closer to their peak — making less sensitive tests, such as at-home tests, more likely to detect the virus.
Now, with the omicron variant, people develop symptoms faster after exposure, in about three days. With people developing symptoms quicker, and thus likely wanting to test sooner, it gives the virus less time to reach levels that are detectable by at-home tests, which are less sensitive than PCR tests.
Simply put: Depending on when you take a test, if you have COVID symptoms and receive negative results from an at-home, rapid test, the level of virus in your body could be too low to be detected by the test, at least at first.
Continuing to test, either through repeat at-home tests or using a PCR test, will give you a better idea of whether you actually have the virus.
If you have COVID symptoms, but test negative, what should you do?
So, if you have COVID symptoms, but received a negative result from an at-home test, what’s next?
As long as you are experiencing symptoms of COVID, Miller suggested following these tips:
▪ Wear a mask when you’re around others. That’s especially important during times of high rates of community transmission of the virus, as we’re experiencing currently.
▪ Continue to re-test at home. Miller suggested continuing to use at-home tests on a daily basis if possible — but if you’re unable to test that frequently, you should at least test on the third and fifth days after you first experienced symptoms.
▪ Seek out a PCR test, especially if you were directly exposed to the virus or you are at high-risk for severe disease or complications from COVID. You can locate COVID testing locations around North Carolina at covid19.ncdhhs.gov/about-covid-19/find-covid-19-tests.
▪ If you know you were exposed to COVID through a direct, close contact, and develop symptoms, you should isolate at home until you can receive additional testing, either through repeat at-home testing or through a PCR test. The Centers for Disease Control offers guidelines for quarantine and isolation at cdc.gov/coronavirus/2019-ncov/your-health/quarantine-isolation.html.
What are the best practices for using at-home COVID tests?
Given all of this information, should you continue to use at-home tests? And are there best practices for doing so, to ensure you get an accurate result?
“At home tests are an excellent way to confirm a symptomatic infection is COVID, if positive,” Miller said. But you should be aware of the information presented here, and understand why a test might come back negative, at least at first, even when you have symptoms.
Miller said the best practices for using at-home COVID tests are:
▪ Follow the directions included provided with the test. Following the directions closely will ensure you’re getting as accurate results as possible.
▪ If your test is negative, but you have symptoms for the virus, you should isolate until you can do additional testing. Additional testing includes repeat at-home testing and seeking out a lab-based PCR test. If you choose to perform repeat testing at home, you should test on the third and fifth days after you first experienced symptoms, if not daily.
▪ If you test positive using an at-home or PCR test, you should follow the CDC’s guidance for quarantine and isolation, which is dependent on whether you are fully vaccinated and other factors.