Observer agreement and clinical significance of chest CT reporting in patients suspected of COVID-19

OBJECTIVES: To assess interobserver agreement and clinical significance of chest CT reporting in patients suspected of COVID-19. METHODS: From 16 to 24 March 2020, 241 consecutive patients addressed to hospital for COVID-19 suspicion had both chest CT and SARS-CoV-2 RT-PCR. Eight observers (2 thoracic and 2 general senior radiologists, 2 junior radiologists, and 2 emergency physicians) retrospectively categorized each CT into one out of 4 categories (evocative, compatible for COVID-19 pneumonia, not evocative, and normal). Observer agreement for categorization between all readers and pairs of readers with similar experience was evaluated with the Kappa coefficient. The results of a consensus categorization were correlated to RT-PCR. RESULTS: Observer agreement across the 4 categories was good between all readers (κ value 0.61 95% CI 0.60–0.63) and moderate to good between pairs of readers (0.54–0.75). It was very good (κ 0.81 95% CI 0.79–0.83), fair (κ 0.32 95% CI 0.29–0.34), moderate (κ 0.56 95% CI 0.54–0.58), and moderate (0.58 95% CI 0.56–0.61) for the categories evocative, compatible, not evocative, and normal, respectively. RT-PCR was positive in 97%, 50%, 31%, and 11% of cases in the respective categories. Observer agreement was lower (p < 0.001) and RT-PCR positive cases less frequently categorized evocative in the presence of an underlying pulmonary disease (p < 0.001). CONCLUSION: Interobserver agreement for chest CT reporting using categorization of findings is good in patients suspected of COVID-19. Among patients considered for hospitalization in an epidemic context, CT categorized evocative is highly predictive of COVID-19, whereas the predictive value of CT decreases between the categories compatible and not evocative. KEY POINTS: • In patients suspected of COVID-19, interobserver agreement for chest CT reporting into categories is good, and very good to categorize CT “evocative.” • Chest CT can participate in estimating the likelihood of COVID-19 in patients presenting to hospital during the outbreak, CT categorized “evocative” being highly predictive of the disease whereas almost a third of patients with CT “not evocative” had a positive RT-PCR in our study. • Observer agreement is lower and CTs of positive RT-PCR cases less frequently “evocative” in presence of an underlying pulmonary disease.