Laboratories and health care providers should not use cycle threshold (CT) values to measure the performance of polymerase chain reaction (PCR) tests for SARS-CoV-2. That was the advice of the American Association of Clinical Chemistry (AACC) in a public statement issued on July 7. And the results of a new study reinforce that the AACC’s recommendation is a sound one. Use of CT Value for Managing COVID-19 Patients According to the Clinical and Laboratory Standards Institute (CLSI), the CT value is the “number of cycles needed for an amplicon to become detectable above background.” Stated differently, the CT value is the lowest PCR cycle number at which the fluorescent probe signal for the amplified target sequence is greater than the minimal detection level determined during validation by the user. Lower CT values are associated with a higher amount of target viral sequence (copy number) in the sample tested. During the pandemic, a number of health care providers and public health agencies have asked laboratories to report the numerical CT value along with the qualitative result when a specimen has detectable SARS-CoV-2 nucleic acids. The AACC’s Opposition The AACC has made it known that it thinks this is a bad idea. […]