Is There a Correlation Between the Cycle Threshold of SARS-CoV-2 RT-PCR and the Clinical Course of COVID-19?

Objectives: Many parameters are studied in coronavirus disease-2019 (COVID-19) to predict the progress of the disease. One of these parameters is the clinical significance of the reverse transcriptase-polymerase chain reaction (RT-PCR) cycle threshold (CT) value used in diagnostic tests. In this study, we evaluated the relationship between RT-PCR CT values and the clinical course of COVID-19. Materials and Methods: Symptomatic patients over the age of 18 years, who had positive severe acute respiratory syndrome-coronavirus-2 RT-PCR test results between June 1, 2020 and December 1, 2020, were screened retrospectively. Patients’ CT values and other data were collected from the hospital’s information management system. Results: The study included the data of 880 patients. The median age was 63 years, and 47% (415) were female. The severity of COVID-19 was mild in 69.7% (614), moderate in 20.4% (180), and severe/critical in 9.7% (86). There was no significant difference between median CT (mCT) levels of disease severity (mCT=22 in mild group; mCT=23 in moderate group; mCT=22 in severe/critical group, p=0.882). The results showed no correlation between these CT values and COVID-19’s severity, prognosis, or laboratory values. Conclusion: Although there are some reports that propose a relationship between CT values and viral load, we believe that these test results cannot be considered quantitative and cannot be generalized because of the many factors known to affect CT values.