Method Description

The covalent stabilization of fibrin by thrombin-activated factor XIII (XIIIa) is the final event in the coagulation of blood. Plasma factor XIII (fibrin-stabilizing factor) zymogen consists of 2 "A" and 2 "B" subunits, the "A" subunits containing an active-center sulfydryl grouping mediating the transamidase activity of the enzyme. The action of thrombin converts fibrinogen to fibrin monomer causing the monomeric molecules to polymerize and be held together by noncovalent hydrogen bonds. These bonds can be broken by 5 M urea or weak acid solutions in the absence of factor XIII. Subsequent to fibrin polymerization by hydrogen bonding, the action of factor XIII results in the formation of covalent bonds that cannot be broken by 5 M urea or weak acid solutions as used in this procedure (1% monochloroacetic acid). Dissolution of a clot by urea or monochloroacetic acid is therefore a qualitative test for factor XIII activity.(Owen CA Jr, Bowie EJW, Thompson JH Jr. Diagnosis of Bleeding Disorders. 2nd ed. Little, Brown and Company; 1975; Meijer P, Verbruggen HW, Spannagl M. Clotting factors and inhibitors: Assays and Interpretation. In: Kottke-Marchant K, David BH. Laboratory Hematology Practice. Wiley Blackwell Publishing; 2012:435-446)