Fitzgerald Trait Plasma is used to detect HMW-kininogen deficiency. HMW-kininogens are plasma glycoproteins involved in the initiation of blood coagulation. A deficiency in HMW-kininogen prolongs the activated partial thromboplastin time (TCA), especially if the reagent used contains silica or kaolin, it is less if the activator used is elagic acid. A deficiency in HMW-kininogen does not cause a bleeding tendency even in the event of deep deficiency.
The prolongation of the TCA can be corrected by the addition of control plasma, plasma deficient in FXII or by the addition of plasma deficient in prekallikrein (Fletcher trait plasma). In addition to this coagulation effect, Fitzgerald Trait Plasma alters fibrinolysis, kinin formation and the permeability of the vascular membrane.