Factor XI


Molecular mass160.000 Da
Half life60 - 80 hours
Plasma concentration2 - 7 mg/l
Normal range70 - 130 %

During the contact activation phase of the intrinsic coagulation system factor XI is bound to negatively charged surfaces together with high molecular weight kininogen (HMWK). Factor XIIa activates bound factor XI. In the next step factor XIa activates factor IX. In plasma, factor XI is bound to HMWK.

Clinical significance

Inherited factor XI deficiency is also know as hemophilia C or Rosenthal syndrome.. Although the condition can affect people of all heritages, it is most common in people of Ashkenazi Jewish descent. The genetic defect is inherited as an autosomal recessive trait. However, the associated bleeding tendency in these patients is low. Liver disease, consumption coagulopathy and DIC lead to an acquired factor XI deficiency. In cases of autoimmune diseases, e.g. Lupus erythematosus, inhibitors against factor XI may be observed. Inhibitors may also be observed after substitution therapy. Recent findings suggest a correlation between increased levels of factor IX and VTE.


  • Suspected inherited factor XI deficiency
  • Suspected factor XI inhibitors
  • Differential diagnosis in patients with Lupus anticoagulants
  • Suspected disorders of the kallikrein-kinin system
  • Diagnosis of thrombophilia


  1. Bouma B, Meijers J. Fibrinolysis and the contact system: A Role for Factor XI in the Down-Regulation of Fibrinolysis. Thromb Haemost 82, 243-250, 1999.
  2. Walsh P. Platelets and Factor XI Bypass the Contact System of Blood Coagulation. Thromb Haemost 82, 234-242, 1999.
  3. Scott CF et al. Amidolytic Assay of Human Factor XI in Plasma: Comparison with a Coagulant Assay and a New Rapid Radioimmunoassay. Blood 63 (1), 42-50, 1984.
  4. Scott CF, Colman RW. A Simple and Accurate Microplate Assay for the Determination of Factor XI in Plasma. J Lab Clin Med 111, 708-714, 1988.
  5. Meijers JCM et al. High levels of coagulation factor XI as a risk factor for venous thrombosis. N Engl J Med 342, 696-701, 2000.
  6. Meijers JCM et al. Inactivation of human plasma kallikrein and factor XIa by protein C inhibitor. Biochemistry 27, 4231-4237, 1988.
  7. Minnema MC et al. Activation of Clotting Factor XI Without Detectable Contact Activation in Experimental Human Endotoxemia. Blood 92, 3294-3301, 1998.
  8. van Montfoort ML, Kuijpers MJ, Knaup VL, Bhanot S, Monia BP, Roelofs JJ, Heemskerk JW, Meijers JC. Factor XI regulates pathological thrombus formation on acutely ruptured atherosclerotic plaques. Arterioscler Thromb Vasc Biol. Aug 34(8), 1668-73, 2014.
  9. Duga S, Salomon O. Congenital factor XI deficiency: an update. Semin Thromb Hemost. Sep 39(6), 621-31, 2013.

Test kits

Chromogenic Assays


UNITEST Factor XIa Inhibitors

ROX Factor XIa

ELISA Complete kit

VisuLize® Factor XI Antigen Kit

Matched-Pair Antibody set