CDC to drop 'gold standard' COVID test: PCR risks false positives

PCR tests, long hailed as the "gold standard" in detecting SARS-Cov-2 cases, will be dropped by the U.S. Centers for Disease Control and Prevention at the beginning of next year. 

Polymerase chain reaction tests have been a mainstay of the U.S. and global response to COVID-19 since early in 2020, but health officials have warned the diagnostic tool poses a risk of false-positive  results.

The test works by amplifying a biological sample through successive cycles until a virus — if it's present in the assay — can be detected by the testing machine. 

The CDC announced this month that it would be withdrawing its request to the U.S. Food and Drug Administration for the emergency use authorization of the test. The agency urged laboratories to "begin their transition to another FDA-authorized COVID-19 test."

CDC spokeswoman Kristen Nordlund told Just the News that the agency was discontinuing its support for the test "given the availability of commercial options for clinical diagnosis of SARS-CoV-2 infection, including multiplexed ... and high-throughput options."

"Although the CDC 2019 Novel Coronavirus ... Real-Time RT-PCR Diagnostic Panel met an important unmet need when it was developed and deployed and has not demonstrated any performance issues, the demand for this test has declined with the emergence of other higher-throughput and multiplexed assays," she said via email. 

Nordlund did not respond to followup queries asking if the risk of false positives had motivated the CDC's discontinuance in any way. 

Those risks have been acknowledged by multiple prominent public health figures, including Dr. Anthony Fauci, chief medical adviser to President Biden and the director of the National Institute of Allergy and Infectious Diseases. 

In a July 2020 interview on an infectious disease podcast, Fauci  warned that the sensitive PCR tests might, if allowed to progress through too many amplification cycles, return a "positive" result when it was actually just detecting "dead nucleotides." 

The World Health Organization earlier this year warned in a medical product alert that PCR tests carry with them the risk of "false positives" because the test might only be picking up small fragments of the virus via heavy amplification.

"[D]isease prevalence alters the predictive value of test results; as disease prevalence decreases, the risk of false positive increases," the alert stated. "This means that the probability that a person who has a positive result (SARS-CoV-2 detected) is truly infected with SARS-CoV-2 decreases as prevalence decreases, irrespective of the claimed specificity."