CO-RADS: A Categorical CT Assessment Scheme for Patients Suspected of Having COVID-19-Definition and Evaluation

Abstract

Background A categorical CT assessment scheme for suspicion of pulmonary involvement of coronavirus disease 2019 (COVID-19 provides a basis for gathering scientific evidence and improved communication with referring physicians. Purpose To introduce the COVID-19 Reporting and Data System (CO-RADS) for use in the standardized assessment of pulmonary involvement of COVID-19 on unenhanced chest CT images and to report its initial interobserver agreement and performance. Materials and Methods The Dutch Radiological Society developed CO-RADS based on other efforts for standardization, such as the Lung Imaging Reporting and Data System or Breast Imaging Reporting and Data System. CO-RADS assesses the suspicion for pulmonary involvement of COVID-19 on a scale from 1 (very low) to 5 (very high). The system is meant to be used in patients with moderate to severe symptoms of COVID-19. The system was evaluated by using 105 chest CT scans of patients admitted to the hospital with clinical suspicion of COVID-19 and in whom reverse transcription-polymerase chain reaction (RT-PCR) was performed (mean, 62 years ± 16 [standard deviation]; 61 men, 53 with positive RT-PCR results). Eight observers used CO-RADS to assess the scans. Fleiss κ value was calculated, and scores of individual observers were compared with the median of the remaining seven observers. The resulting area under the receiver operating characteristics curve (AUC) was compared with results from RT-PCR and clinical diagnosis of COVID-19. Results There was absolute agreement among observers in 573 (68.2%) of 840 observations. Fleiss κ value was 0.47 (95% confidence interval [CI]: 0.45, 0.47), with the highest κ value for CO-RADS categories 1 (0.58, 95% CI: 0.54, 0.62) and 5 (0.68, 95% CI: 0.65, 0.72). The average AUC was 0.91 (95% CI: 0.85, 0.97) for predicting RT-PCR outcome and 0.95 (95% CI: 0.91, 0.99) for clinical diagnosis. The false-negative rate for CO-RADS 1 was nine of 161 cases (5.6%; 95% CI: 1.0%, 10%), and the false-positive rate for CO-RADS category 5 was one of 286 (0.3%; 95% CI: 0%, 1.0%). Conclusion The coronavirus disease 2019 (COVID-19) Reporting and Data System (CO-RADS) is a categorical assessment scheme for pulmonary involvement of COVID-19 at unenhanced chest CT that performs very well in predicting COVID-19 in patients with moderate to severe symptoms and has substantial interobserver agreement, especially for categories 1 and 5. © RSNA, 2020 Online supplemental material is available for this article.

Figure 1.

Cumulative CO-RADS score vs. RT-PCR results and clinical diagnosis. The red columns display cases with a positive RT-PCR result. Yellow columns represent cases with a negative RT-PCR result, but a clinical diagnosis of COVID-19. Green columns display the percentage of cases with a negative RT-PCR result for SARS-Cov-2 and no clinical COVID-19 diagnosis.

Figure 2.

Examples of CO-RADS 3 Axial slices of the basal lungs of two cases with a majority of CO-RADS 3 observations. (A) 72 year-old male with a history of cardiovascular disease and COPD, who presented with fever and a productive cough since one day. He had a negative RT-PCR test for SARS-CoV-2 and a clinical diagnosis of community-acquired pneumonia He was treated with antibiotics and discharged after eight days. (B) 63 year-old female with diabetes, chronic kidney failure and hypertension, who presented with fever and cough since 3 days. RT-PCR was positive for SARS-CoV-2 and she was treated with oxygen therapy and discharged after two days with an advice for quarantine until full resolution of symptoms. Symptoms improved after a few days.

Figure 3.

Examples of CO-RADS 4 Axial slices of the basal lungs of two cases with a majority of CO-RADS 4 observations. (A) 79 year-old male with a history of pulmonary embolism, who presented with a cough since 7 days and fever upon presentation. RT-PCR was positive for SARS-CoV-2, for which the patient was admitted and treated. Patient deceased despite treatment after fourteen days. (B) 78 year old male with a history of COPD, lung cancer and hypertension, who presented with a productive cough and dyspnea since five days, with fever upon presentation. Despite initial negative RT-PCR test for SARS-CoV-2, a clinical diagnosis of COVID-19 was stated based on typical symptoms, CT characteristics and absence of an alternative diagnosis. The patient was discharged and advised to stay in quarantine until full resolution of symptoms.

Figure 4.

Examples of CO-RADS 5 Axial slices of the basal lungs of two cases with CO-RADS 5 observations by all eight observers. (A) 30 year-old female, RT-PCR positive for SARS-CoV-2, who presented with fever and cough since 12 days. Patient was admitted to the COVID-19 ward. She was discharged after seven days, with resolution of symptoms. (B) 51 year-old male, presenting after eight days of fever, dyspnea and cough. A clinical diagnosis of COVID-19 was stated due to clinical symptoms and laboratory findings, despite a negative result at repeated RT-PCR. Patient was admitted for two days due to hypoxia with alleviation of symptoms after five days.