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The wait for a coronavirus test result can vary from less than an hour to a week, depending on the type of COVID-19 test you take. Many people choose the rapid test to get results immediately, but how accurate are these rapid tests?
“Tests that are rapid, typically providing results within 30 minutes, are not as sensitive as the traditional test that is sent to the lab and typically take half a day to several days to get a result,” Dr. Romney Humphries, Ph.D., director of the clinical microbiology laboratory at Vanderbilt University Medical Center, told Fox News.
“The detection rate for rapid tests is 75 to 80%, compared to 90 to 95% with traditional laboratory tests.” Humphries, also a member of the Infectious Diseases Society of America, added.
Humphries added that the rapid test’s ability to correctly identify people with the disease – the sensitivity of the test – may not always be clinically relevant.
“Some studies have shown that rapid tests lacked low levels of the virus. A patient may have low levels of the virus if they are at the onset of infection before the virus has had a chance to replicate, or at the end of the infection when the infection is on its way. disappearance. “
Humphries, also a professor of pathology, microbiology and immunology at Vanderbilt University Medical Center, noted that this could be a potential problem with the spread of the virus.
“In the first case, missing a positive is problematic, because it is a patient who can then infect the others, thinking they are negative. In the latter case, the low virus levels may in fact be dead viruses and this patient may not be infectious. “
Although the wait time for the results of the two tests differs, the technique seems similar in terms of sampling from the nasal passage.
According to the United States Food and Drug Administration (FDA), the antigen test – commonly known as a “rapid diagnostic test” where results are given within minutes to an hour – detects specific proteins on the surface of the virus. It is generally very accurate, although more likely to miss active infection compared to molecular testing, the FDA said on its website.
Some studies have shown that rapid tests lacked low levels of the virus.
Meanwhile, the molecular test, also known as an RT-PCR test, nucleic acid amplification test (NAAT), or diagnostic test, detects the genetic material of the virus and can usually take a day to a week. , depending on laboratory demand. . According to the FDA, this test is very accurate and usually does not need to be repeated. The FDA advises you if you have symptoms but your rapid antigen test is negative, your health care provider may want to order a molecular test to see if you indeed have an active infection.
As for Humphries’ preferred test, “I think the lab test with longer results is the preferable approach, when possible. That being said, there are times when this is not possible and rapid testing in the right context works well, ”she said.
“Rapid tests play an important role and can be very helpful in some cases. For example, a patient who needs trauma surgery cannot wait a day or two for test results because doctors need to know the results before performing a life-saving emergency procedure. Many hospitals use rapid tests for this purpose.
“Another example is screening people before an event – or perhaps using it before going to school – in theory, a rapid test would be useful in these settings, although this rapid testing app would not. is not common, ”added Humphries.
The microbiologist warned that no test is perfect and that everyone has their limits.
“One of the factors that affects every COVID test is getting a really good sample. To collect a suitable nasal pharyngeal sample, the tester must move back enough into the nose to cause a gag reflex, as this is where the coronavirus is located. They need to go deep. Basically, the chances of getting a more accurate test result increase with a better sample, ”she noted.
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