How false negatives are complicating coronavirus testing
This photo is used for illustrative purpose.
Gulf Today Report
As COVID-19 tests become more widely available, scientists have warned about a growing concern: the tests are not 100 percent reliable, meaning people with negative results might actually have the virus.
The majority of tests around the world use a technology called PCR, which detects pieces of the coronavirus in mucus samples.
But "there are a lot of things that impact whether or not the test actually picks up the virus," Priya Sampathkumar, an infectious diseases specialist at Mayo Clinic in Minnesota said.
"It depends on how much virus the person is shedding (through sneezing, coughing and other bodily functions), how the test was collected and whether it was done appropriately by someone used to collecting these swabs, and then how long it sat in transport," she added.
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Different companies around the world are now producing slightly different tests, so it's hard to have a precise overall figure.
Part of the problem lies in locating the virus as its area of highest concentration shifts within the body.
The main nasal swab tests examine the nasopharynx, where the back of the nose meets the top of the throat. This requires a trained hand to perform and some portion of the false negatives arises from improper procedure.
But even if done correctly, the swab may produce a negative.
In these cases, the patient may be asked to try to cough up sputum -- mucus from the lower lungs -- or doctors may need to take a sample more invasively, when a patient is under sedation.
This was done on a patient whose nasal swab returned negative three times, but who showed all the signs of COVID-19.
Eventually, the patient's medical team placed a camera down his windpipe to examine the lungs, then sprayed fluid in and sucked out the secretions, which were then tested, resulting in a positive.
But the real fear of that is people who are given a false negative test and then decide that they're safe to go around their daily life and go out and expose people.
Much hope is placed on newly available serological tests which look for antibodies produced by a person's body in response to the virus and can tell whether a person was infected, long after they recovered.
They could also be used to help diagnose a person who is currently infected but whose PCR test results showed a false negative, by waiting a week or so for the body to produce its immune response.
"We are excited about the serologic test, but we don't know how well it will work and we are starting to study it," said Sampathkumar.
