Fig 1: Serum levels and ROC curves of CHI3L1 and IGFALS as determined by ELISA assays. (A) In 15 COVID-19 patients with adverse prognosis, the median serum levels [interquartile range, IQR] of CHI3L1 and IGFALS were 136.2 [67.41–357.2] ng/mL and 1.479 [0.6873–3.059] µg/mL, respectively. In 46 COVID-19 patients with favorable prognosis, the median serum levels [IQR] of CHI3L1 and IGFALS were 49.87 [32.04–89.04] ng/mL and 4.498 [2.565–6.342] µg/mL, respectively. In 30 healthy controls, the median serum levels [interquartile range, IQR] of CHI3L1 and IGFALS were 24.3 [19.66–28.0] ng/mL and 8.396 [7.424–9.464] µg/mL, respectively. Differences in continuous values between the two groups were compared by the Mann–Whitney U-test: ***p < 0.001, ****p < 0.0001. These analyses were carried out with GraphPad Prism software. (B) ROC curves for predicting the clinical prognosis of severe COVID-19 patients. The optimal cut-off values (sensitivity and specificity) for making a clinical decision using CHI3L1 or IGFALS were defined as 60.01 ng/mL (0.867 and 0.600) and 3.28 µg/mL (0.867 and 0.689), respectively. The p-values were generated from bootstrap tests for the two ROC curves. AUC indicates the area under the ROC curve [95% CI].