Factor XIII, a fibrin stabilizing factor, is a clotting factor that helps in final blood coagulation to form cross-linking fibrin, stabilizing blood clots. It is synthesized in the liver, and deficiency causes unstable blood clots prone to premature breakdown. Assays evaluate solubility, ammonia release or chromogenic study, finding the ability to cross-link fibrin. The test is indicated in bleeding disorders, miscarriage, and healing delay.