False-negative results on RT-PCR

Reverse-transcriptase polymerase chain reaction (RT-PCR) tests provide little diagnostic value immediately after SARS-CoV-2 exposure. The probability of false-negative results is 100% on the day of exposure, falling to 38% when symptoms begin roughly 4 days later and then to 20% at 3 days after symptom onset. Then it begins to increase again. In the Annals of Internal Medicine, the researchers conclude: “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. 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.”

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