Comparison of the polymerase chain reaction and computed tomography performed in the emergency department in patients with suspected COVID-19

Accurate diagnosing SARS-CoV-2 infected patients is crucial for effective disease control. However, the clinical presentation of Covid-19 is often unspecific, and the majority of patients are asymptomatic or have mild symptoms. Although RT-PCR is the gold standard in diagnosis, RT-PCR sometimes may not be sufficient to decide in isolation, due to the prolonged time to get the test result and the high false-negative rate in emergency departments. This study aimed to find out the diagnostic performance of CT, which was categorized according to RSNA recommendations in the emergency department, compared to the standard test RT-PCR. Between 01.03-2020 and 30.09.2020, 324 patients were admitted to the emergency department and were evaluated as suspicious for Covid-19, and to whom both RT-PCR test and chest CT imaging were performed for various indications were included. All chest CT scans were grouped into four different categories according to RSNA recommendations by two blinded radiologists. Considering the RT-PCR test result as a gold standard, the diagnostic performance of CT was calculated according to different threshold categories. The observers' agreement was compared using Kappa analysis, and the final CT category of the patients that radiologists evaluated differently was determined by Latent Cluster analysis. Of the 324 patients (Median age, 66; IQR, 29), 112 (35%) were RT-PCR positive. There was a good agreement (κ: 0.76) according to the RSNA classification between the two radiologists. The final CT category was typical for 35% of the patients. Eighty-nine patients (%80) with confirmed Covid-19 had typical CT category, and the rate of RT-PCR positivity was significantly higher in patients whose CT was regarded as typical category, compared to other categories. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated as 66%, 81%, 65%, 82%, and 76% when the typical category threshold was accepted. When indeterminate and atypical categories were set as the threshold, sensitivity increased, but other test results decreased. There were 20 (13%) patients who were considered negative in the first RT-PCR however were found to be positive for Covid-19 on repeated tests. Considering this result, the first RT-PCR's sensitivity and negative predictive value were calculated as 69% and 87%. CT of 60% of the patients evaluated as false negative was in the typical category. Although CT is not a suitable tool for the diagnosis and screening of Covid-19 due to its low specificity, the use of CT in the diagnosis of patients who have already scanned with CT seems to be a reasonable option in emergency departments. The use of the RSNA classification is reproducible and safe.