What is factor XII deficiency?

Updated: Oct 06, 2020
  • Author: Irene S Pakos, DO; Chief Editor: Perumal Thiagarajan, MD  more...
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Factor XII deficiency is defined as an absence or reduced level of blood coagulation factor XII (Hageman factor). Factor XII initiates the intrinsic coagulation cascade and is linked to the fibrinolytic, kallikrein-kinin, and complement systems. [131] It promotes the conversion of factor XI to its activated form. Factor XII deficiency typically occurs in the absence of a patient or family history of hemorrhagic disorders and is marked by prolonged clotting time.

Halbmayer et al have estimated the prevalence of severe and mild factor XII deficiency to be 1.5-3%. [132] This group has identified an association between factor XII deficiency and coronary artery disease. Measurements of plasma factor XII activity, fibrinogen, and lipoprotein in 426 consecutive patients with coronary heart disease awaiting cardiac surgery found 44 (10.3%) were moderately deficient in factor XII (factor XII activity, 17-50%; antigen, 15-57%). The prevalence of factor XII deficiency was significantly higher (P< .0001) among patients with coronary heart disease than among 300 similarly evaluated healthy blood donors (2.3%).

Factor XII deficiency has not been linked to any significant hemorrhagic diatheses. The disorder may be considered in patients with prolonged aPTT, normal PT, normal bleeding time, and no clinical history of bleeding. Once thought likely, the deficiency can be confirmed by normalization of aPTT with plasma component therapy and by factor assay.

Factor XII deficiency has clinical significance when attempts are made to heparinize individuals who have this condition. Routine coagulation tests used during cardiopulmonary bypass return abnormal findings in patients with factor XII deficiency and are useless for monitoring anticoagulation in these patients. Alternative monitoring systems, such as chromogenic heparin assay, citrated thrombin time, and recalcified thrombin time, must instead be used. [133]

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