Chest CT Accuracy in Diagnosing COVID-19 During the Peak of the Italian Epidemic: A Retrospective Correlation with RT-PCR Testing and Analysis of Discordant Cases

Abstract Objectives The goal of this study was to assess chest computed tomography (CT) diagnostic accuracy in clinical practice using RT-PCR as standard of reference. Methods From March 4th to April 9th 2020, during the peak of the Italian COVID-19 epidemic, we enrolled a series of 773 patients that performed both non-contrast chest CT and RT-PCR with a time interval no longer than a week due to suspected SARS-CoV-2 infection. The diagnostic performance of CT was evaluated according to sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and diagnostic accuracy, considering RT-PCR as the reference standard. An analysis on the patients with discrepant CT scan and RT-PCR result and on the patient with both negative tests was performed. Results RT-PCR testing showed an overall positive rate of 59.8%. CT sensitivity, specificity, PPV, NPV, and accuracy for SARS-CoV-2 infection were 90.7% [95% IC, 87.7% to 93.2%], 78.8% [95% IC, 73.8-83.2%], 86.4% [95% IC, 76.1% - 88.9%], 85.1% [95% IC, 81.0% - 88.4] and 85.9% [95% IC 83.2-88.3%], respectively. Twenty-five/66 (37.6%) patients with positive CT and negative RT-PCR results and 12/245 (4.9%) patients with both negative tests were nevertheless judged as positive cases by the clinicians based on clinical and epidemiological criteria and consequently treated. Conclusions In our experience, in a context of high pre-test probability, CT scan shows good sensitivity and a consistently higher specificity for the diagnosis of COVID-19 pneumonia than what reported by previous studies, especially when clinical and epidemiological features are taken into account.