Fig. 3.

Metabolites associated with the disease severity of COVID-19. (A) The OPLS-DA scores plot of SD vs. MD. The Y axis represents orthogonal T score, and the X axis represents T score; (B) The volcano plot of SD vs. MD. Red dots represent the up-regulated metabolites (log₂FC ≥ 1, VIP ≥ 1); blue dots represent the down-regulated metabolites (log₂FC≤-1, VIP ≥ 1); gray dots represent metabolites without significant changes (-1 < log₂FC < 1, VIP ≤ 1). (C) The KEGG analysis of the DEMs in SD vs. MD. (D) The important metabolites prioritized by xgboost analysis. (E) Receiver operating characteristic (ROC) and performance of the xgboost model in the test sets. (F) The heatmap of 13 metabolites in SD vs. MD. (G) The correlation heatmap of DEMs. (H) the raw intensity of cyclamic acid and N-Acetylneuraminic acid