• Jeremy Harman

Tested Negative For COVID-19? You May Want To Double Check That...


Image courtesy of Glen Carrie, Unsplash.com

You’ve just gotten your COVID-19 test results back; negative. Excellent news, but you’re not out of the woods just yet. Enter, false negative test results.


First, an explanation of the term ‘false negative’. A false negative result means a patient is given a ‘negative’ test result and told they do not have COVID-19 when in actuality they are infected and contagious. This is a growing concern among healthcare professionals as false-negative results can contribute to further outbreaks of the coronavirus, should an asymptomatic individual who has falsely tested negative relax their social distancing measures. The risk of false negatives are inevitable, but the risk can be reduced by using proper swabbing techniques when swabbing for COVID-19.



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As with most respiratory viruses, the COVID-19 virus is believed to be most concentrated in the nasopharynx. “...[nasopharyngeal swab tests] are generally accepted as the gold standard method for respiratory viruses due to the lymphoid tissue in the adenoid bed.” states Dr. Leigh Sowerby, ENT Surgeon at London Health Sciences Centre and Western University’s Department of Otolaryngology. To get the most accurate sample possible, a nasal swab must go deep into the nasal cavity (roughly the distance from their nostril to the opening of the ear), to the nasopharynx, and collect specimens for 5 - 10 seconds before removing the swab. This procedure is quick and painless, however can be slightly uncomfortable to patients due to the location of the nasopharynx.


COVID-19 patients were found to have a one in five chance of getting a negative test result during their infection even if they were actually positive. If a swab test does not reach the nasopharynx it is more likely to provide a false-negative test result.

According to a recent study by the Annals of Internal Medicine from researchers at Johns Hopkins university, COVID-19 patients were found to have a one in five chance of getting a negative test result during their infection even if they were actually positive. If a swab test does not reach the nasopharynx it is more likely to provide a false-negative test result. The New England Journal of Medicine recently published a paper reinforcing that while COVID-19 testing capacity is an issue, the accuracy of the test is actually of greater long-term concern. Microbiologist Kelly MacDonald states in a CBC article that if a swab test does not reach the nasopharynx, it is more likely that there will be a false negative result.


Image courtesy of the United Nations, Unsplash.com

Another factor is the incubation period and timing of the COVID-19 test. Infectious disease expert Dr. Anna Banerji states in a CBC articleI believe we are massively underreporting cases," and a spokesperson for the Public Health Agency of Canada adds “A low viral load, which can occur in the very early stage of the disease or during the recovery phase, could give a false negative result." Therefore, it seems some false negative results are a result of a test being performed too early, or too late. If any patients continue experiencing symptoms similar to COVID-19, it is recommended to act as if you are infected and self-isolate for 2 weeks to avoid potentially infecting others.




In conclusion, false negative test results are likely to occur in approximately 20 percent of nasal swab tests. Performing accurate nasopharyngeal swab tests is currently the most effective way to reduce the likelihood of false negative results. If you are experiencing any COVID-19 symptoms, call your doctor or 911 immediately to seek help and get tested as soon as possible.




References:

https://www.acpjournals.org/doi/10.7326/M20-1495

https://www.nejm.org/doi/full/10.1056/NEJMp2015897?query=TOC

https://www.cbc.ca/news/canada/manitoba/covid-19-false-negatives-1.5532595

https://www.ecdc.europa.eu/en/covid-19/latest-evidence/diagnostic-testing

https://www.cbc.ca/news/health/coronavirus-test-false-negative-1.5610114


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