RESUMO
Activated by calcium and thrombin, factor XIII (FXIIIa) cross-links fibrin, thus increasing the stability of the fibrin clot. Furthermore, the hemostatic and reparative function of factor XIIIa is mediated by cross-linking other proteins like alpha(2)-plasmin-inhibitor, fibronectin, and collagen. The FXIII Val34Leu polymorphism plays a role in athero- and thrombogenesis. FXIII deficiency is an autosomal recessive disorder. The most common symptom is the bleeding tendency of the umbilical cord some days after birth. The diagnosis is confirmed by a solubility clot test in urea (5 mol/l) and then differentiated with an incorporation assay and immuno-electrophoresis. The bleeding tendency typically becomes obvious when FXIIIa activity is <1-2%. Severe bleeding episodes, however, may even occur with FXIIIa activities of 30-50%, especially in heterozygous persons. The sometimes life-threatening bleeding tendency of the inherited FXIII deficiency can be treated with FXIII concentrates. Acquired FXIII deficiency occurs in several internal diseases and after major surgery. The clinical significance is not completely clear. Moreover, FXIII is applied locally as a component of fibrin glues.