Kininogen-1, also known as high molecular weight kininogen, Williams-Fitzgerald-Flaujeac factor, Alpha-2-thiol proteinase inhibitor, Fitzgerald factor, KNG1, and BDK, is a secreted protein that contains three cystatin domains. Kininogen-1 / KNG1 is a protein from the blood coagulation system as well as the kinin-kallikrein system. It is a protein that adsorbs to the surface of biomaterials that come in contact with blood. Kininogen-1 / KNG1 circulates throughout the blood and quickly adsorbs to the material surfaces. Kininogen-1 / KNG1 is one of the early participants of the intrinsic pathway of coagulation, together with Factor XII (Hageman factor) and prekallikrein. Kininogen-1 / KNG1 is one of the kininogens, a class of proteins. As with many other coagulation proteins, the protein was initially named after the patients in whom deficiency was first observed. When the clinical data were combined, it turned out that all patients had a deficiency of the same protein. Defects in KNG1 are the cause of high molecular weight kininogen deficiency (HMWK deficiency) which is an autosomal recessive coagulation defect. Patients with HWMK deficiency do not have a hemorrhagic tendency, but they exhibit abnormal surface-mediated activation of fibrinolysis.