CT-severity score in COVID-19 patients: for whom is it applicable best?

Background: lung involvement in COVID-19 can be quantified by chest CT scan. We evaluated the triage and prognostication performance of seven proposed CT-severity score (CTSS) systems in two age groups of >= 65 and <65 years old. Methods: Confirmed COVID-19 patients by reverse transcriptase polymerase chain reaction (RT-PCR) admitted from February 20th, 2020 to July 22nd were included in a retrospective single center study. Clinical disease severity at presentation and at peak disease severity were recorded. CT images were scored according to seven different scoring systems (CTSS1-CTSS7). The cohort was divided into two age groups of >= 65 and <65 years old. Receiver operator characteristic (ROC) curves for each age group for diagnosis of severe/critical disease on admission (for triage) were plotted. Such curves were also plotted for predicting severe/critical disease at peak disease severity (for prognostication), and critical disease at peak severity (for prognostication). Areas under the curve (AUCs), best thresholds, and corresponding sensitivities (Sens.) and specificities (Spec.) were calculated. Results: 96 patients were included with a mean age of 63.6 +/- 17.4 years. All CTSSs in 65-year-old or more group (N=55) showed excellent performance (AUC.80-0.83, Sens.+Spec.= 155-162%) in triage and excellent or outstanding performance (AUC.810.92, Sens.+Spec.= 153-177%) in prognostication. In the younger group (N=44), all CTSSs were unsatisfactory for triage (AUC.49-0.57) and predicting severe/critical disease (AUC.67-0.70), but were acceptable for predicting critical disease (AUC.70-0.73, Sens.+Spec.= 132-151%). Conclusion: CTSS is an excellent tool in triage and prognostication in patients with COVID-19 >= 65 years old, but is of limited value in younger patients.