|Molecular mass||80 000 Da|
|Half life||40 - 50 hours|
|Plasma concentration||15 - 47 mg/l|
|Normal range||50 - 150% or 0.5 - 1.5 U/ml|
Factor XIIa is the central enzyme of the contact activation phase of the intrinsic coagulation system. Binding of the proenzyme factor XII to negatively charged surfaces results in its activation to factor XIIa, which in turn activates prekallikrein to kallikrein. In a positive recoupling mechanism, kallikrein again activates factor XII. The coagulatory effect of factor XIIa is the activation of factor XI. In addition to the procoagulant effect of factor XIIa, the formation of kallikrein simultaneously results in both an activation of the fibrinolytic system and the kallikrein-kinin system.
Hereditary factor XII deficiency is very rare. Acquired deficiencies may occur in connection with liver disease, increased consumption during DIC, lupus anticoagulants, nephrotic syndrome and rejection reactions. Increased factor XII concentrations are observed during pregnancy and in women taking oral contraceptives.
- Suspected inherited factor XII deficiency
- Suspected factor XII inhibitors
- Differential diagnosis in patients with Lupus anticoagulants
- Suspected disorders of the kallikrein-kinin system
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