Clinical measurements of SP-D primarily support that the total circulating SP-D can be used to correct for the background variation in SP-D in interstitial lung diseases or to facilitate differentiation of idiopathic pulmonary fibrosis from other idiopathic interstitial pneumonias when included into a multi-marker array (15, 304, 487). Here, SFTPD is linked to idiopathic pulmonary fibrosis.