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Factor XII (Hageman).
Last reviewed: 05.07.2025
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Reference values (norm) of factor XII activity in blood plasma are 65-150%.
Factor XII, also known as the Hageman factor, is an important component of the human blood clotting system. The factor was named after John Hageman, a patient who was found to be deficient in the factor in 1955, causing his blood to take longer to clot in laboratory tests. Despite this, Hageman and other people with factor XII deficiency do not have an increased tendency to bleed, indicating its unique role in the blood clotting process.
Factor XII is a precursor (prozymogen) that is activated upon contact with damaged surfaces or external substances, such as negatively charged surfaces. When activated, factor XII initiates a cascade of reactions that leads to the formation of an active serine protease, factor XIIa. Factor XIIa plays a key role in the initiation of the intrinsic pathway of the blood coagulation system, activation of prekallikrein and the kininogen system, and interactions with the fibrinolysis and complement systems, which emphasizes its importance in inflammatory and reparative processes in the body.
Interestingly, abnormalities associated with factor XII rarely lead to clinically significant conditions. Factor XII deficiency is not associated with an increased risk of bleeding, unlike deficiencies of other coagulation factors. However, some studies have shown that abnormalities in factor XII can affect the risk of thrombosis, inflammatory conditions, and some other pathological processes, although the mechanisms of these relationships are not fully understood.
In clinical practice, factor XII level analysis may be prescribed when investigating the causes of blood coagulation disorders, as well as as part of a comprehensive assessment of hemostasis before surgical interventions or in conditions where there is a suspicion of a blood coagulation disorder.
Factor XII (Hageman) is a sialoglycoprotein activated by collagen, contact with a foreign surface, adrenaline, and a number of proteolytic enzymes (in particular, plasmin). Factor XII initiates intravascular coagulation; in addition, factor XIIa converts plasma prekallikreins into kallikreins. Active factor XII serves as an activator of fibrinolysis.
Factor XII deficiency is characterized by increased clotting time and APTT without signs of bleeding. In clinical practice, factor XII activity testing is used primarily to detect its congenital deficiency. Factor XII deficiency should be suspected when clotting time and APTT are significantly increased. In most cases, Hageman defect is inherited in an autosomal recessive manner. There is a strict correspondence between the degree of blood clotting disorder and factor XII deficiency: in severe hypocoagulation, the activity level of this factor in plasma does not exceed 2% and is often below 1%; in moderate clotting disorder, it ranges from 3 to 9%. If factor XII activity in plasma is 10% or more, the clotting time, APTT, and other tests are normal.
Acquired factor XII deficiency characterizes consumption coagulopathy due to DIC.
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