Incidental Detection of Factor XII Deficiency Following Coronary Artery Bypass Grafting

Coagulation Factor XII (fXII), the Hageman factor, is a procoagulant 80kDa glycoprotein with a plasma concentration of about 40 µg/mL (approximately 500 nmol/L). Plasma fXII is mainly synthesized in the liver, but the leukocyte form of the protein has been recently recognized. fXII is the plasma zymogenic form of the serine protease factor XIIa. When the fXII zymogen encounters the negatively charged surface, it is autoactivated and the serine protease fXII (F XIIa) becomes activated. fXII activates a procoagulant and proinflammatory contact system that drives the kallikrein-kinin system and the internal coagulation pathway. Zymogen fXII also stimulates endothelial cell proliferation, neoangiogenesis, and wound healing; as well as adhesion, migration, and chemotaxis of neutrophils and thus plays a role in the inflammatory response. fXII deficiency occurs very rarely, with an incidence of about 1/1,000,000 individuals. It is usually inherited in an autosomal recessive fashion, although an autosomal dominant type of inheritance has been described.

Adequate and careful titration of protamine to reverse heparinization and timely thromboprophylaxis in these patients is necessary given the uncertainty regarding thrombosis occurrence. The authors’ patient was administered protamine for the reversal of anticoagulation at a dose of 300 mg during slow intravenous infusion, and directly postoperatively LMWH was titrated based on the weight of the patient. There were no thrombotic complications during intraoperative and immediate postoperative flow.

In conclusion, fXII deficiency is a very rare disorder that is manifested by elevated aPTT and ACT values. Timely diagnosis, adequate perioperative coagulation monitoring, and postoperative prophylaxis with LMWH will minimize the occurrence of complications.