A negative test on a little plastic at home test for COVID-19 is less comforting as the pandemic enters its fourth anniversary.
You still have to swab your nose before you go to dinner parties. Wait 15 minutes, then text your host “negative!” before you leave your KN95 mask behind.
It seems like the right thing.
The virus has mutated and again . However, the tests offer some control over the growth of the Greek letters. Experts warn against trusting a negative outcome.
It’s fitting that we do a reality check of what these rapid COVID-19, also known as antigen tests can do, and what they can’t.
Are the new omicrons causing problems with at-home testing?
The majority of the time, the answer to this question is no.
Scientists are seeing changes in spike protein as the virus evolves. This is because the virus attacks healthy cells and uses it to its advantage. However, the rapid antigen testing aren’t looking for spike protein.
Dr. Colgrove says that the tests rely on the detection of the nucleocapsid proteins, which is the protein directly encapsulating viral RNA. Robin Colgrove is a Harvard Medical School professor and chair of the Diagnostics Committee of the Infectious Diseases Society of America.
He claims that this internal protein has not changed much over time as the virus has evolved. The rapid tests are able to detect it, at least temporarily.
The situation is being monitored by federal health agencies in the event of any changes. As the virus evolves, the Food and Drug Administration and the National Institutes of Health are collaborating to examine how the at-home testing works.
The agencies have only identified one test so far — the Luminostics Inc. Clip COVID Rapid Antigen Testing — This test has become less reliable due to new variants. Even so, FDA states that “the impact doesn’t appear to be substantial.”
Is it taking longer for antigen tests to give a positive result?
Some people report negative antigen test results that persist for days despite being exposed to COVID-19 and showing other symptoms. They eventually test positive but sometimes it takes up to a week.
Colgrove says that the phenomenon is somewhat mysterious. Colgrove acknowledges that doctors have seen it, but it is still a mystery.
He asks, “What kinda experiment would you need to conduct to answer that question?” and then explains that it would be hard to study.
Dr. Baird says that home tests may be taking longer to register positive results. For example, the virus could multiply faster in other places than the nostrils of some patients. Geoffrey Baird is the chair of the Department of Laboratory Medicine and Pathology, University of Washington School of Medicine.
Baird believes that human error is the greatest factor. People who do these tests at home can make mistakes and aren’t as trained as those who do COVID-19 in a laboratory.
He says that there will be people who put it in their mouths. This is because not everyone follows the instructions. Many people mistakenly believe that mucus from the swab will contain lots of virus. “Actually, you don’t want any snot on it.”
While people are more likely to get positive antigen tests around the time they become infected, Baird states that it is important to keep in mind that there will always be people who test positive sooner than others and those who test negative later.
These tests actually work.
Although antigen tests are useful in some situations (more details in a moment), Baird emphasizes that they do have limitations. This was true even before the pandemic.
He says that similar technology for influenza has been around for many years, and it was recommended not to use them.
Antigen tests are used to identify specific proteins in the virus. The tests are typically performed by swabbing the nostrils. It takes about 15 minutes for a positive or neutral result. These at-home tests require more virus to produce a positive result than a PCR (which is performed in a laboratory and allows for trace amounts of viral gene material to “amplify” over time, usually a few days. Even if there is not much virus, it should still trigger a positive result. PCR tests can also continue to be positive even after the patient has been cleared.
Each type of test has its advantages and disadvantages. There are two types of measures that can be used to measure test performance: specificity and sensitivity .
Specificity refers to how well the test can detect false positives. Sensitivity is the ability of the test to detect the virus.
Both PCR and antigen tests can be used to detect false positives. However, PCR tests are more sensitive than home tests. Antigen tests can’t be used to rule out COVID-19. However, they can be useful in confirming that the cold is COVID-19.
Antigen tests are not able to determine if you have symptoms. Researchers also found this when they examined more than 100 antigen test studies and published their findings to the Cochrane Database of Systematic Reviews in July.
They wrote that rapid antigen tests were less accurate in those who don’t have any signs or symptoms, but perform better when people are in close contact with people who have confirmed COVID-19.
These same researchers found that not all home test results were equal. They reviewed 49 types of tests.
Jacqueline Dinnes, lead author at the University of Birmingham stated that there was a lot of variation between brands of tests. “Our overall results combine findings of different studies that evaluated similar tests,” she said in a podcast.
What are these tests really good for?
Experts say it’s not the way the COVID-19 tests were intended to be used.
Colgrove states that a positive test almost always proves true. Colgrove says that if a person has been exposed or shows signs of illness, they can take a test to confirm their diagnosis. Your diagnosis is now complete.
It’s a different story for those who are able to get over COVID-19, and want to test to see if they’re still positive.
According to the Centers for Disease Control and Prevention , a negative result “doesn’t rule out” COVID-19. A person who tests negative for COVID-19 should take another test within 48 hours to determine if the result is positive. The FDA recommends that a person with a known COVID exposure or other symptoms take a second test 48 hours later.
It is important to understand the limits of the tests and to follow the instructions to retesting if you receive a negative result.
Colgrove states, “In a person with suggestive symptoms now in the middle of an epidemic where the prevalence is high, a single positive test is not sufficient to rule out infection.”
Even if you don’t have COVID-19 symptoms it is a good idea not to worry and stay at home.
Copyright 2023 NPR. Copyright 2023 NPR.
