Background and aim: Increased alveolar concentration of nitric oxide (CA(NO)) is related to the severity of interstitial lung disease (ILD) in systemic sclerosis (SSc). However, cut-off levels of CA(NO) to rule out, or to rule in, the presence of ILD in individual patients are unknown. We aimed to assess the validity of CA(NO) for the diagnosis of ILD in SSc and to determine the thresholds of CA(NO) that can be used in clinical practice to predict the likelihood of ILD in SSc.
Methods: Lung HRCT scan, PFTs and partitioned exhaled NO measurements were performed in 65 consecutive SSc patients. ILD was diagnosed on pulmonary HRCT according to the presence of ground glass or reticular opacities. Diagnostic performance of CANo for ILD diagnosis was assessed using ROC curves.
Results: 38 out of 65 SSc patients had ILD. CA(NO), at a cut-off level of 4.3 ppb, had a sensitivity and specificity for the diagnosis of ILD of 87% (95% CI: 77 to 99) and 59% (95% CI: 41 to 78), respectively. The same cut-off level of CA(NO) could detect impairment of gas exchange with a sensitivity and specificity of 78% (95% CI: 67 to 90) and 73% (95% CI: 46 to 99), respectively. Moreover, ILD could be ruled in (positive predictive value > 95%) when CA(NO) > or = 10.8 ppb, and ruled out C(ANO) values < or = 3.8 ppb (negative predictive value > 95%).
Conclusion: CA(NO) could be a valid non-invasive biological marker of ILD in SSc, and be of use in clinical practice.