Be Wary of False-Negatives in RT-PCR COVID-19 Tests
By David Doolittle

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Reverse transcriptase polymerase chain reaction (RT-PCR) tests, which have been commonly used to diagnose COVID-19, have a high chance of false negative results, especially at early onset of infection, researchers at Johns Hopkins Medicine have found.

In a report published May 13 in the Annals of Internal Medicine, researchers said the chances of a false negative – when a virus is not detected in a person who is or recently has been infected – is greater than 20% and, at times, far higher. 

False negatives were more common early in an infection, leading researchers to conclude RT-PCR tests add little diagnostic value in the days immediately after exposure.”

The meta-analysis, which looked at data from seven studies, found that over the four days of infection before the typical time of symptom onset (Day 5), the probability of a false negative decreased from 100% on Day 1 to 67% on Day 4. The probability decreased to 20% on Day 8, three days after symptom onset but then began to increase again, from 21% on Day 9 to 66% on Day 21.

“Care must be taken in interpreting RT-PCR tests for SARS-CoV-2 infection – particularly early in the course of infection – when using these results as a basis for removing precautions intended to prevent onward transmission,” researchers said. “If clinical suspicion is high, infection should not be ruled out on the basis of RT-PCR alone, and the clinical and epidemiologic situation should be carefully considered.”

If you have questions about the types of tests that are available as well as their purposes, limitations, restrictions, and potential risks, the Texas Medical Association COVID-19 Task Force created a “how to” testing guide that covers topics including the basics of PCR (molecular), serology (antibody), point-of-care, and at-home tests.

The guide serves as a supplement to the much more comprehensive frequently asked questions (FAQ) document on testing that the Task Force published.

Find both documents, along with the latest news, resources, and government guidance, on TMA’s COVID-19 Resource Center, which is updated regularly.

Last Updated On

May 28, 2020

Originally Published On

May 28, 2020

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