Health

How Confident Can You Be in a Coronavirus Test?

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Many coronavirus test results already say “detected” or “not detected” as the default display, a distinction that several experts call more useful.

“‘Not recognized’ really indicates the moment,” said Dr. Valerie Fitzhugh, a pathologist at Rutgers University. “It wasn’t discovered today. That doesn’t mean I won’t have it tomorrow. “

Called some tests molecular testsLook for the genetic material or RNA of the coronavirus. (Whether done with a nasal swab or saliva, these tests are generally considered reliable, especially when done in a laboratory using a technique called a polymerase chain reaction, or PCR.) Antigen testsInstead, look for pieces of coronavirus proteins or antigens. Antigen tests tend to be faster, but worse, than molecular tests to identify coronavirus cases, especially when the virus is present in relatively small amounts, so someone can be RNA positive but antigen negative.

This can occur because the virus is on its way out of the body or because most of it has not gained a foothold. However, it is also possible that antigen tests fail to identify the virus in its upswing in the early days of infection.

Updated

Dec. 24, 2020 at 9:46 am ET

Such mismatched results have forced the word “negative” to play a myriad of roles: “Negative” for antigen doesn’t always mean “negative” for the virus, confusing and frustrating people who had hoped to declare themselves infection-free.

Using terms like “positive” and “negative” that could create outdated stereotypes about sexually transmitted infections could also discourage people from sharing their status with others or following isolation guidelines, said Hannah Getachew-Smith, a health communications expert at Northwestern University. However, a detection mindset could help “separate tests from my life and myself.”

No test is perfect. But the likelihood of one false positive or a False negative can vary dramatically depending on the circumstances under which a test was performed. The two most important of these are people’s recent health history and the spread of the virus in their community. Scientists call the confluence of these factors Pre-test probability.

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