https://www.cdc.gov/coronavirus/2019-ncov/lab/testing.html

Updated Aug. 5, 2020

About the Testing, interesting article

PCR TESTS

Before laboratories use a new test on samples from patients, they must verify the test performance (make sure it works as expected) using “positive” and “negative” control materials. The positive control should always test positive, and the negative control should always test negative. During validation of the CDC SARS-CoV-2 test, some laboratories discovered a problem with one of the test’s three reagents—chemicals required to run a test. The reagent produced a positive result with the negative control, so laboratories could not verify test performance.

To resolve the issue, CDC laboratories determined that this reagent could be left out without affecting test accuracy because of the built-in redundancy in test design.

The redundant design saved time by allowing the kits to be used without the reagent. FDA authorized this modification, and new test kits with the two necessary reagents were manufactured and distributed to states. These kits are still in use.