Fig. 1.

Receiver operating characteristic curve analyses of serum biomarker levels at diagnosis. The curves show the power of LDH (A), ferritin (B), sIL2-R (C), KL-6 (D), and D-dimer (E) levels for evaluating COVID-19 severity, respectively. The arrows indicate the cut-off values. The optimal cut-off values of LDH, ferritin, sIL2-R, KL-6, and D-dimer levels at diagnosis were 265 U/L, 770 ng/mL, 929 U/mL, 303 U/mL, and 2.7 μg/mL, respectively. At the cut-off values, serum KL-6 level had a sensitivity of 76.2% and a specificity of 86.2% in evaluating disease severity. LDH: lactate dehydrogenase, sIL2-R: soluble interleukin-2-receptor, KL-6: Krebs von den Lungen-6, AUC: area under the curve.