Chest x-ray severity score in COVID-19 patients on emergency department admission: a two-centre study

Background: Integration of imaging and clinical parameters could improve the stratification of COVID-19 patients on emergency department (ED) admission. We aimed to assess the extent of COVID-19 pulmonary abnormalities on chest x-ray (CXR) using a semiquantitative severity score, correlating it with clinical data and testing its interobserver agreement. Methods: From February 22 to April 8, 2020, 926 consecutive patients referring to ED of two institutions in Northern Italy for suspected SARS-CoV-2 infection were reviewed. Patients with reverse transcriptase-polymerase chain reaction positive for SARS-CoV-2 and CXR images on ED admission were included (295 patients, median age 69years, 199 males). Five readers independently and blindly reviewed all CXRs, rating pulmonary parenchymal involvement using a 0-3 semiquantitative score in 1-point increments on 6 lung zones (range 0-18). Interobserver agreement was assessed with weighted Cohen's kappa, correlations between median CXR score and clinical data with Spearman's rho, and the Mann-Whitney U test. Results: Median score showed negative correlation with SpO(2) (rho = -0.242, p < 0.001), positive correlation with white cell count (rho = 0.277, p < 0.001), lactate dehydrogenase (rho = 0.308, p < 0.001), and C-reactive protein (rho = 0.367, p < 0.001), being significantly higher in subsequently dead patients (p = 0.003). Considering overall scores, readers' pairings yielded moderate (kappa = 0.449, p < 0.001) to almost perfect interobserver agreement (kappa = 0.872, p < 0.001), with better interobserver agreement between readers of centre 2 (up to kappa = 0.872, p < 0.001) than centre 1 (kappa = 0.764, p < 0.001). Conclusions: Proposed CXR pulmonary severity score in COVID-19 showed moderate to almost perfect interobserver agreement and significant but weak correlations with clinical parameters, potentially furthering CXR integration in patients' stratification.