These clotting proteins activate the early phase of the intrinsic pathway and the complement system. When decreased, they may prolong PTT but not PT. They do not depend on vitamin K carboxylation.
Normal ranges:
High molecular weight kininogen: 59 " “135%
Prekallikrein: 55 " “207%
Interpretation
Decreased In
Extremely rare congenital deficiencies
No bleeding diathesis associated with deficiencies; reflected in prolonged PTT