Ct values as a diagnostic tool for monitoring SARS-CoV-2 viral load using the QIAstat-Dx® Respiratory SARS-CoV-2 Panel. (September 2022) - Juanola-Falgarona, Martí
Highlights: Use of the cycle threshold value as a proxy of viral load with patient outcomes is under debate. The QIAstat-Dx SARS-CoV-2 assay has a linear range spanning from 10 6 to 10 2 cp/mL. Limit of detection for SARS-CoV-2 assay remains unaffected by genetic variability. Cycle threshold values could help making clinical and patient-management decisions. Abstract: Objectives: Qualitative real-time polymerase chain reaction tests are not designed to provide quantitative or semiquantitative results because cycle threshold (Ct) values are not normalized to standardized controls of known concentration. The aim of this study was to characterize SARS-CoV-2 viral loads based on Ct values, using the QIAstat-Dx® Respiratory SARS-CoV-2 Panel. Methods: Different lineages of SARS-CoV-2 clinical samples and the World Health Organization international standard were used to assess the linearity of the QIAstat-Dx Respiratory SARS-CoV-2 Panel. Limit of detection for the different lineages was characterized. Results: Comparable efficiencies and linearity for all samples resulted in R 2 ≥0.99, covering a dynamic range of 1, 000, 000-100 copies/mL for the SARS-CoV-2 assay, showing linear correlation between Ct values and viral load down to 300 copies/mL. Conclusion: The SARS-CoV-2 Ct values provided by the QIAstat-Dx® Respiratory SARS-CoV-2 Panel could be used as a surrogate for viral load given the linear correlation between Ct values and viral concentration down to limit of detection. This panel allows to obtain reproducible Ct values for SARS-CoV-2 ribonucleic acid downstream of the sample collection, reducing the sample-to-Ct workflow variability. Ct values can help provide a reliable assessment and comparison of viral loads in patients when tested with the QIAstat-Dx Respiratory SARS-CoV-2 Panel.