New method flags false positives in COVID-19 test results

A registered nurse stirs a nasal swab in testing solution after administering a COVID-19 test at Sameday Testing on July 14, 2021 in Los Angeles, California. (Credit: Mario Tama/Getty Images)

Researchers have developed and tested a process to identify potential false positive COVID-19 test results.

They say the method could help prevent unnecessary quarantining and repeated testing of people who are not actually infected.

COVID-19 testing is an important tool for managing the virus during the pandemic, and reverse transcriptase polymerase chain reaction (RT-PCR) testing is the most widely used method. But while this type of test is considered reliable, it is associated with a small number of false positive results, most easily recognized in asymptomatic, nonexposed patients.

False positive diagnoses have important implications for patient management,” says Lester Layfield, professor of pathology and anatomical sciences and director of the Molecular Diagnostics Laboratory at the University of Missouri. “False positives may lead to inappropriate quarantine, delay of other necessary medical treatment, or transfer to a COVID-19 ward.”

To help ensure the accuracy of positive tests, Layfield developed a protocol for repeat testing of all positive results involving asymptomatic and unexposed patients, and in all cases in which a specimen with a positive result was located in a testing well next to another specimen with a high virus load.

Layfield and colleagues implemented the quality control protocol in September 2020. Over an eight-week period, they performed 24,717 RT-PCR tests. Of those, 6,251 came from asymptomatic patients. In that group, 288 specimens initially returned a positive result. A second test revealed 20 of these to be false positives.

“Retesting of positive results from asymptomatic individuals revealed some technologist errors but also contamination from positive specimens in adjacent specimen wells,” Layfield says. “This study should alert the laboratory testing community of the possibility of false positive COVID-19 tests.”

The study appears in the Journal Pathology-Research and Practice. The authors declare they have no conflict of interest to report in relation to this study.

Source: University of Missouri