Factor XIIIa (fibrin-stabilising factor)
Fibrin and control · Transglutaminase Normal PT/APTT
A transglutaminase activated by thrombin in the presence of calcium. It forms covalent epsilon-(gamma-glutamyl)lysine bonds between adjacent fibrin gamma and alpha chains and cross-links alpha-2-antiplasmin onto the mesh, making the clot strong and lysis-resistant. Because it acts only after a clot has already formed, every routine coagulation test is normal in its absence.
Traced from the start
- Tissue factor and the extrinsic triggerVitamin K cycle and gamma-carboxylation
- Contact activation system (factor XII, prekallikrein, high-molecular-weight kininogen)
- Subendothelial collagen and von Willebrand factor
- Tissue factor-factor VIIa complex (extrinsic tenase)Factor IXaFactor VIIIa and its von Willebrand factor carrierActivated platelet phospholipid surface
- Factor XaFactor VaProthrombin (factor II)
- Thrombin (factor IIa)
- Factor XIIIa (fibrin-stabilising factor)
Detail
- Activated by
- Thrombin plus calcium
- Action
- Transglutaminase forming gamma-glutamyl-lysine cross-links between fibrin D-domains; also incorporates alpha-2-antiplasmin and fibronectin into the clot
- Screening test
- Urea clot solubility — a clot that dissolves in 5 mol/L urea indicates severe factor XIII deficiency; confirm with a factor XIII activity assay
- Not detected by
- PT, APTT or thrombin time, all of which are entirely normal
When it goes wrong
Congenital factor XIII deficiency, autosomal recessive and rare
Delayed bleeding from the umbilical stump in the neonate, poor wound healing, recurrent miscarriage and a high lifetime risk of spontaneous intracranial haemorrhage — all with a completely normal coagulation screen, so it must be requested specifically
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