The coagulation cascade is a diagram used to describe the interactions and activations that occur to the coagulation factors. These interactions occur on the surfaces of the platelets. These interactions and activations are all occurring so that fibrin (factor Ia) can be formed from the activation of fibrinogen (factor I). Many laboratory professionals have learned the coagulation cascade as two separate pathways - “extrinsic” and “intrinsic” - that result in the activation of a final “common” pathway. The common pathway is the final set of reactions that produces fibrin (factor Ia) from fibrinogen (factor I).
- Newer research has shown that the EXTRINSIC pathway starts most blood coagulation due to the activity of factor III (tissue factor). Be aware that tissue factor is also known as thromboplastin, which is the reagent added to a patient sample in the prothrombin time (PT) assay. The intrinsic pathway is believed to be more of a supplement to the extrinsic pathway.
The coagulation factors are mostly proteins made in the liver, with the exception being calcium and tissue factor. Thus, liver damage that results in decreased protein production results in varying degrees of decreased coagulation ability, due to the loss of coagulation factor production.