High Molecular Weight Kininogen (HMWK) is a multifunctional plasma protein primarily synthesized by hepatocytes. As the precursor to bradykinin, HMWK plays a central role in the kallikrein-kinin system, where it is cleaved by plasma kallikrein to release bradykinin, a peptide that mediates vasodilation, increased vascular permeability, and pain signaling. Beyond its role as a bradykinin precursor, HMWK functions as a critical cofactor in the intrinsic pathway of blood coagulation, facilitating the activation of factors XI, XII, and prekallikrein. Additionally, HMWK acts as a major extracellular cysteine proteinase inhibitor, helping to regulate protease activity and protect tissues from excessive proteolysis.