SFTPD and idiopathic pulmonary fibrosis: Also, among patients with IPF, there was a stronger correlation between the serum HO-1 and the serum SP-D (r=0.73, p=0.002) and between the serum HO-1 and the GGO score (r=0.59, p=0.020) (Figures 2(c) and 2(d)).