Protein C inhibitor (PCI; SERPINA5) is a plasma serine protease inhibitor, and a potent inhibitor of activated protein C (APC), which plays a critical role in the anticoagulant protein C pathway. Recently, PCI was also found to form a complex with the serine protease hepatocyte growth factor activator (HGFA), inhibiting the HGFA-catalyzed activation of the single-chain hepatocyte growth factor precursor.