Coagulation

The coagulation cascade is usually divided into three areas depending
On the initiating cause of activation:
Intrinsic Pathway, Extrinsic pathway and Common pathway.

The intrinsic pathway is initiated when blood contacts a rough surface
(e.g. collagen).

The extrinsic pathway is initiated by Thromboplastin from damaged cells.

Both pathways activate the common pathway which ends with a clot.

aPTT PT
Intrinsic pathway
(rough surface)		 Extrinsic pathway
(Tissue Thromboplastin)
Factor XII
Factor XI
Complex of
Factor IX, VIII and PF-3 		Factor VII
Common pathway
Complex of Factor V, X and PF3
Prothrombin
Fibrinogen
Clot


Available lab tests to evaluate coagulation:

PT – Prothrombin Time – measures the extrinsic pathway

Factors of the extrinsic pathway are activated by the incubation of
plasma with Thrombopastin and a phospholipid. If any of the
coagulation factors is absent, a prolongation of clotting time will occur.

aPTT- Activated thromboplastin time – measures the intrinsic pathway

Factors of the intrinsic pathway are activated by the incubation of
plasma with a surface activator and a phospholipid.
If any of the coagulation factors is absent, a prolongation of clotting
time will occur.

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