SFTPD and idiopathic interstitial pneumonia: The areas under the ROC curves for IPF patients in comparison with control subjects were 0.988 for napsin A, 0.938 for KL-6, 0.931 for SP-A, and 0.940 for SP-D, with serum napsin A levels showing the greatest area, however, there were no significant differences in AUC values between serum napsin A and the other markers.