Serum Rcn3 level is a potential diagnostic biomarker for connective tissue disease-associated interstitial lung disease and reflects the severity of pulmonary function

Background: Although reticulocalbin 3 (Rcn3) has a critical role in alveolar epithelial function as well as in pathogenesis of pulmonary fibrosis, no study has yet examined its diagnostic and prognostic values for interstitial lung disease (ILD). This study aimed to evaluate Rcn3 as a potential marker for differential diagnosis in the patients with idiopathic pulmonary fibrosis (IPF) and connective tissue disease-associated interstitial lung disease (CTD-ILD) and reflecting the severity of disease. Methods This was a retrospective observational study included 71 ILD patients and 19 healthy controls. These patients were stratified into IPF group (39) and CTD-ILD group (32). The severity of ILD was evaluated through pulmonary function test. Results Serum Rcn3 levels were statistically higher in CTD-ILD patients than those in IPF patients (p = 0.012) and healthy controls (p = 0.028). There were statistic negative correlations between serum Rcn3 and TLC, FVC and DLCO in patients with CTD-ILD (r = -0.367, p = 0.039; r = -0.391, p = 0.027; r = -0.370, p = 0.037, respectively), but not in IPF patients. ROC analysis demonstrated that serum Rcn3 had superior diagnostic value for CTD-ILD and an Rcn3 cutoff value of 2.73 ng/mL had a sensitivity of 69%, a specificity of 69% and an accuracy of 45% for diagnose of CTD-ILD. Conclusions Serum Rcn3 levels might be a clinically useful biomarker in screening and evaluating CTD-ILD.