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Last April, the U.S. Food and Drug Administration granted emergency approval for the first at-home diagnostic test for COVID-19. Now, they're being sold at pharmacy chains. 

But you may want to think twice before relying on the test, especially if you get a negative result.

Dr. Bryan McIver, Deputy Physician-in-Chief

Dr. Bryan McIver, Deputy Physician-in-Chief

“There has been legitimate concern around false negative test results for COVID-19,” said Dr. Bryan McIver, deputy physician-in-chief at Moffit Cancer Center. “There is a false negative rate in all of medicine; there is no perfect test. But with what we have seen with COVID-19, the false negative rate has more to do with sample collection than the actual test.”

For the at-home test, patients will swab their own nose and mail the sample to a laboratory. A simple nasal swab may not detect COVID-19 because it cannot reach where the virus is predominately found, and could result in a false negative test. That is especially the case in someone at the early stage of the disease, where the amount of the virus is likely to be low.

Instead, a sample should be taken from a patient’s nasopharynx, the upper part of the throat behind the nose.

“If you want to pick up the virus for those who people who do not have symptoms, you would certainly need to do a nasopharynx swab,” said McIver. “This is not something you would do yourself, but rather it would be done by a medical professional wearing proper protective gear.”

Moffitt has its own COVID-19 screening clinic that tests patients for the virus before they undergo treatment, procedures and surgeries. The sample is collected with a nasopharynx swab and is then sent to the lab for analysis.

Test accuracy is determined by looking at the number of patients who test negative for the virus who indeed do not have it. The chance of receiving a false negative result in Moffitt’s COVID-19 screening clinic is less than 1 in 1,000.

“If a patient gets a positive result in our screening clinic we are postponing surgery or treatment if we can, and if there is a negative result we know with 99.9% accuracy they don’t have COVID-19 and we are comfortable going through with surgery or treatment,” said McIver.