The clinical significance of real-time PCR cycle threshold (Ct) values in Clostridioides difficile infection

Clostridioides difficile infection (CDI) is a common gastrointestinal infection associated with significant morbidity and mortality worldwide, particularly following antibiotic use. Polymerase chain reaction (PCR)-based diagnostic methods are widely used, and the evaluation of cycle threshold (Ct) values as an additional marker for predicting clinical severity has gained increasing interest. The aim of this study was to investigate the diagnostic and prognostic value of PCR Ct values in distinguishing severe from non-severe CDI when evaluated together with clinical and demographic characteristics.

In this retrospective study, adult patients (≥18 years) with C. difficile (tcdA/tcdB) detected by the QIAstat-Dx® GI2 Panel (QIAGEN, Hilden, Germany) between January 2024 and December 2025 were evaluated. Ct values were analyzed together with clinical and demographic data, and risk factors for severe CDI were assessed using logistic regression and receiver operating characteristic (ROC) analyses.

Of the 80 patients with CDI, 38.7% were classified as having severe CDI. Ct values were significantly lower in the severe CDI group compared with the non-severe group (28.1 ± 3.6 vs. 30.8 ± 3.1; p < 0.05). In multivariable analysis, Ct value and the Charlson Comorbidity Index (CCI) were identified as independent risk factors for severe CDI. Each one-unit increase in Ct value was associated with a 20.5% reduction in the risk of severe CDI, while each one-point increase in CCI approximately doubled this risk.

In conclusion, PCR Ct values, when interpreted together with comorbidity burden, may be a useful tool for predicting severe CDI and may contribute to clinical decision-making.