Diagnostic Value of NO-Related Biomarkers (ADMA, NO, eNOS) in Stable COPD and Acute Exacerbation of COPD

Background: Nitric oxide (NO)-related biomarkers, including asymmetric dimethylarginine (ADMA), nitric oxide (NO), and endothelial nitric oxide synthase (eNOS), may play a role in the pathophysiology and clinical progression of chronic obstructive pulmonary disease (COPD). This study aimed to investigate their diagnostic value in stable COPD and acute exacerbation. Methods: A total of 150 participants (76 females, 74 males; mean age 53.82 ± 7.06 years) were enrolled and equally distributed into control, stable COPD, and acute exacerbation groups (n = 50 each). Demographic, clinical, and laboratory parameters were compared across groups. Serum ADMA, NO, and eNOS levels were analyzed, and correlations with clinical findings were evaluated. ROC analysis was performed to determine the diagnostic performance of the biomarkers. Results: Serum ADMA levels were significantly higher in COPD patients, particularly in the acute exacerbation group (p < 0.05 for all comparisons). In contrast, NO and eNOS levels were significantly lower in COPD groups compared to controls (p < 0.05 for all comparisons). ADMA showed strong negative correlations with FEV₁, FEV₁/FVC, PaO₂, and SaO₂, whereas NO and eNOS showed positive correlations with the same parameters (all p < 0.01). For predicting acute exacerbation, an ADMA cut-off of 1.36 yielded high diagnostic accuracy (AUC = 0.983; sensitivity 86.0%; specificity 96.0%). eNOS also demonstrated predictive value (AUC = 0.823). For stable COPD, NO at a cut-off of 14.91 showed excellent diagnostic performance (AUC = 0.921). Conclusions: NO-related biomarkers, particularly ADMA and NO, may serve as reliable indicators for differentiating between stable COPD and acute exacerbation. Elevated ADMA and reduced NO and eNOS levels were closely associated with impaired lung function and oxygenation parameters. These findings suggest potential clinical utility of these biomarkers in COPD monitoring and management.