Normal factor XIII activity is generally about 70–140% (roughly 0.7–1.4 IU/mL), though some labs use ranges near 50–150%, so check your lab’s reference. Levels below about 50% raise bleeding risk; severe congenital deficiency is usually under 5%, causing spontaneous bleeding and poor wound healing. Assessment uses FXIII activity assays and antigen testing; treatment depends on severity.

Factor XIII, the fibrin‑stabilizing factor, is a plasma transglutaminase circulating as an A2B2 tetramer. Thrombin and calcium activate the A subunits to factor XIIIa, which cross‑links fibrin strands, stabilizing clots and resisting fibrinolysis. It also supports wound healing and pregnancy. Congenital or acquired deficiency causes delayed bleeding, poor wound repair and recurrent pregnancy loss.

The factor XIII test measures the activity or amount of coagulation factor XIII, which stabilizes fibrin clots. It is ordered for unexplained bleeding, poor wound healing, recurrent pregnancy loss, or abnormal clot stability. Testing uses clot-solubility screening or quantitative activity/antigen assays on blood; abnormal results prompt genetic testing and specialist referral for diagnosis and treatment planning.

The 13 clotting factors are: Factor I (fibrinogen), II (prothrombin), III (tissue factor/thromboplastin), IV (calcium), V (proaccelerin/labile factor), VII (proconvertin/stable factor), VIII (antihemophilic factor A), IX (Christmas factor), X (Stuart–Prower factor), XI (plasma thromboplastin antecedent), XII (Hageman factor), XIII (fibrin‑stabilizing factor). They act sequentially to form and stabilize a fibrin clot during hemostasis.

Factor XIII deficiency is treated with regular replacement using factor XIII concentrate (recombinant or plasma-derived), given intravenously as prophylaxis—typically every 3 to 4 weeks—to prevent bleeding. For acute bleeds or before surgery, additional or higher doses are given. If specific concentrate is unavailable, cryoprecipitate or fresh frozen plasma may be used; acquired cases also need treatment of the underlying cause.

High factor VIII increases risk of venous thrombosis (DVT, pulmonary embolism) and of recurrent clots. It can be an acute‑phase finding (infection, inflammation, pregnancy, surgery, estrogen therapy), so repeat testing when well. Management depends on personal clot history and risk factors: evaluate for thrombophilia, treat reversible causes, and consider anticoagulation or preventive measures if clinically indicated. Lifestyle and medical risk modification are important.