The American Association for Clinical Chemistry (AACC) has issued a public statement advising against the use of cycle threshold (Ct) values from SARS-CoV-2 tests to guide care for patients with COVID-19.
The association’s move follows a decision by the Association for Molecular Pathology (AMP) and the Infectious Diseases Society of America (IDSA) in April to urge caution in the use of Ct values for clinical decision-making.
With a PCR SARS-CoV-2 test, a low Ct value generally indicates a high amount of virus in a sample while a high Ct value indicates a low amount of virus, which the AACC said has led some researchers to speculate whether the Ct values could help identify patients at risk for serious illness. However, in a statement detailing the limits of these Ct values, the AACC said that “even though Ct values correlate with the amount of virus in specific specimens, studies have not actually established a relationship between Ct values and a patient’s overall viral load or infectiousness.”
There are also numerous factors aside from the amount of virus in a specimen that can impact the Ct values generated during coronavirus testing, such as a patient’s age and the test instruments used, the AACC said.
“If clinical laboratories decide to report Ct values to clinicians who request them, the association recommends that labs include a prominent comment with every report explaining that the use of Ct values to guide patient management is discouraged and why,” the AACC said.