Fig. 4

Receiver operating characteristic curve analyses of initial and peak values of serum biomarkers for predicting poor prognosis, defined as requiring IMV over 28 days or death in COVID-19 patients requiring supplemental oxygen or IMV. Initial value was defined as the first value obtained within the 3rd day of hospitalization, and peak value was defined as the highest value obtained during the entire hospitalization. Among the initial values, the optimal cut-off values of KL-6 (a), LDH (b), and D-dimer (c) were 412 U/mL (sensitivity 64.1%, specificity 70.4%), 408 U/L (55.3%, 65.7%), and 1.85 ng/mL (64.1%, 66.7%), respectively. Among the peak values, the optimal cut-off values of KL-6 (d), LDH (e), D-dimer (f), and ferritin (g) were 966 U/mL (81.6%, 84.3%), 556 U/L (86.8%, 82.4%), 16.2 ng/mL (71.1%, 72.2%), and 1152 U/L (50.0%, 65.4%), respectively. KL-6 Krebs von den Lungen-6, LDH lactate dehydrogenase, AUC area under the curve, IMV invasive mechanical ventilation