In the COVID-19 testing industry, there are two clearly defined standards of tests. The PCR (polymerase chain reaction) test is the gold standard in COVID-19 testing. Although the PCR test is highly accurate, it is not perfect. The other industry-standard of COVID-19 testing is the Rapid Antigen test. The COVID-19 Rapid Antigen test produces fast results, but those results are not as accurate as those of the PCR test. The COVID-19 Rapid Antigen test often yields false-negative and false-positive results.

Outside of imperfections in COVID-19 testing, understanding the lifecycle of a COVID-19 infection can help explain false negatives in COVID-19 PCR testing and help avoid them. From the initial point of contact, there is a latent period when the virus lays dormant in a person’s system. In this latent period, a person cannot transmit the virus to others, nor will they test positive for the COVID-19 virus. In this instance, a false negative test result occurs.

So, although the COVID-19 PCR test is highly accurate, the probability of detecting the virus depends on timing in the viral infection lifecycle. As mentioned previously, first, there is the latent period of infection. A person will not test positive for the COVID-19 virus during the latent period, and this causes several COVID-19 PCR test false negatives. Following the latent period comes the incubation period of the COVID-19 viral infection. The length of the COVID-19 virus incubation period on average is roughly five or six days. However, the COVID-19 virus incubation period can be up to 14 days in some instances. During the incubation period, people can become infectious two or three days before showing symptoms of a COVID-19 infection. For this reason, the spread of the COVID-19 virus is so prevalent.

Since people do not start showing symptoms for two or three days after the COVID-19 virus is transmittable to others, they often fail to self-isolate or quarantine until it is too late. People often do not take COVID-19 PCR tests until they are showing symptoms. At this point, they have already come into contact with several others and infected other people with the COVID-19 virus. People aren’t aware they have the COVID-19 virus and spread it to others.

According to a scientific medical study estimating the false-negative rate by day since infection, the rate a COVID-19 virus-infected individual tests false negative on the day they contracted the virus was 100%. On the fourth day of COVID-19 viral infection, the false-negative rate was 67%. On the fifth day, the COVID-19 false-negative rate was 38%. Even after eight days from the initial COVID-19 virus infection, the COVID-19 false-negative rate was 20%. Eight days is sometimes into some showing symptoms for two or three days. Considering these numbers, waiting five to six days after coming into contact with another COVID-19 positive person is critical to getting the most accurate results while avoiding false-negative COVID-19 PCR test results. You can review the study “Variation in False-Negative Rate of Reverse Transcriptase Polymerase Chain Reaction–Based SARS-CoV-2 Tests by Time Since Exposure” at the Annals of Internal Medicine.