How The Risk Of False Negative Tests For COVID-19 Changes Over Time

How the risk of false negative tests for COVID-19 changes over time

The authors of the new study calculated the risk of an incorrect result for each day, starting from the day of infection with the virus.

Tests for the SARS-CoV-2 coronavirus are used, among other things, to detect the virus in people at risk: among medical workers and people who have come into contact with patients with COVID-19. Therefore, it is very important to understand how accurate the tests are between infection and symptoms.

In a new study, published in the Annals of Internal Medicine, scientists described the sensitivity of PCR tests for SARS-CoV-2 coronavirus by day, starting from the day of infection.

The authors of the scientific work analyzed data from 7 previous studies, which contained information on the indications of tests (swabs from the upper respiratory system) for coronavirus in various periods after infection. In total, the analysis covered the data of 1330 people.

According to the data obtained, the probability of a false negative test result decreases from 100% (four days before the appearance) to 67% in one day (before the development of the clinical picture) and to 38% (on the first day of "visible illness").

Three days after the onset of symptoms of COVID-19, the probability of a false negative test result was 20%, but then it began to grow again - up to 66% on the 16th day of illness.

Scientists note that interpret the results of PCR tests for SARS-CoV-2 infection with caution. This is especially important when their results are used to decide on the lifting of restrictive measures that prevent further spread of infection. If the suspicion of COVID-19 is high, then the decision should not be made on the basis of this analysis alone.