A process that initiates the intrinsic pathway of coagulation. In vitro FXII can be activated to FXIIa through contact with a variety of negatively charged surfaces such as kaolin, sulfatides, micronized silica, or ellagic acid. Key players are FXII and Prekallikrein both of which require HK as a cofactor in their conversions from zymogens to active serine proteases.
