Neutrophil extracellular traps (NETs) play a role in inflammatory amplification, vascular endothelial injury, and immune thrombosis in Behçet’s disease (BD). However, whether NETs-related biomarkers can serve as stable and reliable indicators of disease activity remains to be determined. We aimed to examine the association of circulating NETs score with disease activity of patients with BD.

In this retrospective observational study, we enrolled 160 adult (aged >18 years) patients diagnosed with BD, 24 patients with Adult‑onset Still’s disease (AOSD), and 111 healthy controls. Blood samples were collected to detect cell-free DNA, MPO-DNA, NE-DNA, and citH3-DNA complexes. A composite NETs score was generated based on the four indicators. Based on the NETs score, BD patients were further classified into high-NETs and low-NETs subgroups using unsupervised clustering analysis.

The levels of cell-free DNA and NET-DNA complexes were significantly elevated in patients with BD compared with healthy controls and were further increased in active versus inactive disease. Treated patients showed lower levels of MPO-DNA, NE-DNA, and citH3-DNA complexes than untreated patients, whereas cell-free DNA levels did not differ significantly between the two groups. The composite NETs score was significantly higher in patients with active BD and correlated with inflammatory burden, including CRP (ρ=0.34), ESR (ρ=0.22), IL-6 (ρ=0.38), TNF-α (ρ=0.37), IL-1β (ρ=0.47), and IL-18 (ρ=0.53). The NETs score outperformed individual NET-DNA complexes in discriminating active from inactive BD (AUC=0.754) and showed excellent discrimination between BD and healthy controls (AUC=0.973). Multivariable logistic regression analysis showed that each 1-SD increase in the NETs score was independently associated with active Behçet’ s disease and major organ involvement (adjusted OR 1.48, 95% CI 1.05-2.13, P=0.029; and adjusted OR 3.02, 95% CI 1.95-4.97, P<0.001, respectively). Consistently, patients with high NETs scores were more likely to have active disease (89% vs 50%, P<0.001) and major organ involvement (69% vs 47%, P=0.035).

Our findings revealed that the NETs score was elevated in active BD and was positively associated with an increased risk of major organ involvement. These findings suggest an increased NET burden in patients with BD and provide a clinical basis for further investigation into the inflammatory pathways associated with key NETs fraction.