(in-trin'zik kō-ag'yū-lā'shŭn path'wā) A part of the coagulation pathway that is activated by contact of coagulation proteins with negatively charged surfaces. All components are within the bloodstream and include factors XII, XI, IX, VII, HMWK, and prekallikrein. The activated partial thromboplastin time tests for abnormalities in this pathway.