Table 2.
Key dysregulated metabolic pathways and discriminatory metabolites in community-acquired pneumonia (CAP) compared with healthy controls
| Pathway | Metabolite | VIP value | Fold change | Log2 FC | AUC |
|---|---|---|---|---|---|
| Glyoxylate & dicarboxylate metabolism / TCA | Malate or Malic acid | 3.374 | 2.591 | 1.373 | 0.790 |
| Aromatic amino acid metabolism | 4-Hydroxybenzeneacetic acid (4-HPAA) | 2.459 | 27.97 | 4.806 | 0.855 |
| Propanoate metabolism | 2-Hydroxybutyrate | 2.059 | 4.779 | 2.256 | 0.793 |
| Aromatic amino acid metabolism | 4-Hydroxyphenyllactic acid | 1.882 | 20.67 | 4.369 | 0.731 |
| Tryptophan metabolism | Indole-3-acetic acid | 1.742 | 10.53 | 3.39 | 0.730 |
| Ketone body metabolism | 3-Hydroxybutyrate | 1.66 | 7.14 | 2.83 | 0.764 |
| Cystine & Methionine metabolism | 2-Ketobutyrate | 1.61 | 2.59 | 1.376 | 0.768 |
| Arachidonic acid metabolism | Arachidonic acid | 1.59 | 2.05 | 1.04 | 0.650 |
| Amino-acid / Propanoate metabolism | Methylmalonate | 1.436 | 3.974 | 1.991 | 0.722 |
Legend: Metabolites are ordered according to decreasing Variable Importance in Projection (VIP) scores derived from orthogonal partial least squares–discriminant analysis (OPLS-DA). VIP values reflect the relative contribution of each metabolite to group separation, with higher values indicating greater discriminatory importance. Fold change (FC) represents the ratio of metabolite abundance in community-acquired pneumonia (CAP) patients relative to controls. In contrast, log₂ fold change (log₂FC) indicates the direction and magnitude of change on a logarithmic scale. The area under the receiver operating characteristic (ROC) curve (AUC) reflects the diagnostic performance of individual metabolites in distinguishing CAP from controls, with higher values indicating greater discriminative ability