In a study on 33 IPF patients and 44 controls, no significant differences were observed in the circulating levels of free and total protein S in IPF patients compared with healthy individuals [81], while in another study, lower plasma concentrations of protein S were detected in a small cohort of 11 patients affected by IPF if compared to 20 healthy controls [82]. Here, PROS1 is linked to idiopathic pulmonary fibrosis.