Cycle threshold values and SARS-CoV-2: Relationship to demographic characteristics and disease severity

Cycle threshold (Ct), or the number of cycles required to amplify viral RNA to a detectable level, provides an estimate of viral load. Previous studies have demonstrated mixed results in regard to the association between SARS-CoV-2 Ct from real-time reverse transcriptase PCR (rRT-PCR) testing to patient outcomes, and there is less data on the relationship between Ct and patient characteristics. This was a retrospective study of 256 patients tested at a tertiary care emergency department from March to July 2020 via nasopharyngeal rRT-PCR testing utilizing the Abbott M2000 SARS-CoV-2 assay. Kruskal-Wallis, univariable, and multivariable logistic regression were used where appropriate for analysis. There were no significant differences in Ct value by demographic characteristics including age, sex, race, or ethnicity. Ct increased with time since symptom onset (p < 0.001), and increasing Ct was associated with increased odds of severe disease (odds ratio: 1.05, 95% confidence interval: 1.0-1.11). Ct was not found to be associated with patient demographic characteristics and increasing Ct was found to be associated with increased odds of severe disease. Continued study will allow us to better comprehend the complex factors that contribute to the risk for severe outcomes due to SARS-CoV-2 infection.

Automated summary

In this study, it was found that Ct value is not associated with demographic characteristics, but increases with time since symptom onset in SARS-CoV-2 infection. Additionally, increasing Ct value is associated with increased odds of severe disease.