Prekallikrein, high molecular weight kininogen and Factor XII are the contact factors involved in initiation of coagulation. Deficiencies of prekallikrein and/or high molecular weight kininogen are rare.
Inheritance of deficiencies: autosomal recessive
Clinical features: No history of abnormal bleeding.
Laboratory findings:
(1) normal PT
(2) markedly prolonged aPTT
(3) normal assays for XII, XI and other coagulation factors
(4) decreased kinin formation and fibrinolysis
(5) correction of the aPTT by addition of normal plasma
Features of prekallikrein deficiency:
(1) correction of the prolonged aPTT following exposure of the plasma to glass (or kaolin)
(2) decreased plasma levels on specific assay
Features of high molecular weight kininogen deficiency:
(1) decreased plasma levels on specific assay
(2) some patients also have a deficiency of low molecular weight kininogen
(3) some patients also have a deficiency in prekallikrein
NOTE: Reliable assays for prekallikrein and high molecular weight kininogen may be difficult to find.
