Pentraxin-3 as a diagnostic and prognostic biomarker in inflammatory lung diseases.

Inflammatory lung diseases, including community-acquired pneumonia, acute respiratory distress syndrome (ARDS), severe viral pneumonia (including COVID-19), ventilator-associated pneumonia, and exacerbations of chronic obstructive pulmonary disease (COPD), necessitate prompt diagnostic and prognostic assessments accompanied by microbiological confirmation of the causative pathogen. Conventional biomarkers, including C-reactive protein and procalcitonin, are insufficient to distinguish between localized pulmonary and systemic inflammation. This narrative review summarizes the studies on Pentraxin-3 (PTX3), a locally synthesized, extrahepatic acute-phase protein secreted by endothelial cells, epithelial cells, and myeloid leukocytes at sites of inflammation, as a diagnostic and prognostic biomarker in the continuum of inflammatory lung diseases. Plasma PTX3 indicates systemic endothelial activation and disease severity, whereas bronchoalveolar lavage PTX3 concentrations provide compartment-specific diagnostic data, identify follow-up infections, and allow therapeutic escalation in relation to the disease phenotype. Nevertheless, clinical laboratory implementation involves matrix-specific reference levels, analytical validation containing limits of detection/quantification, precision, linearity, and interfering studies according to CLSI, commutable calibrators, and traceability hierarchies. The pre-analytical procedure is standardized, and platform-independent decision limits through harmonized assays, preparation of external quality assessment, and compatibility of acute-care turnaround times are required to implement multicenter PTX3 in routine clinical laboratory diagnostics.