High Molecular Weight Kininogen and Prekallikrein (Fletcher Factor)

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