SFTPD and interstitial lung disease: Subgroup analyses showed that serum SP-D levels in the ILD group were significantly higher than in the non-ILD group (WMD= 21.02 ng/mL, 95% CI: 11.68-30.37, p<0.001), whereas serum SP-D levels in the ILD group were remarkably higher compared with the healthy control (HC) group (WMD= 263.78 ng/mL, 95% CI: 215.98-311.58, p<0.001) (Figure 2).