Serum Rcn3 further showed statistically negative correlation with pulmonary function indexes (TLC% pred and DLCO% pred) and positive correlation with inflammatory indexes (CRP and ESR) (r =  − 0.367, p = 0.039; r =  − 0.370, p = 0.037; r = 0.355, p = 0.046; r = 0.392, p = 0.026, respectively) in CTD-ILD patients rather than IPF patients. This evidence concerns the gene RCN3 and idiopathic pulmonary fibrosis.