**2. Coagulation pathways**

Coagulation requires complex interactions of cellular and molecular components, mainly involving platelets, plasma and red blood cells. The process was classically described as a cascade of 'Intrinsic', 'Extrinsic', and 'Common' pathways (see Figure 1). These pathways

The Intrinsic Pathway is activated when FXII binds to exposed collagen of damaged endothelium. The cascade of activations occur as shown, and amplification also occurs (for example FXIIa converts prekallikrien to kallikrien and auto-activates more FXII). The resulting "Tenase" complex (shown in a dashed yellow line) activates FX. The Extrinsic Pathway is initiated by Tissue Factor, and results in a TF/FVIIa complex (in a dashed yellow line) that activates FX. The Common Pathway yields thrombin (FIIa), which not only activates Fibrinogen (FI) but also amplifies other stages of the cascade by activating FVIII, FV and FXIII. The ultimate result is a cross-linked Fibrin mesh. HMWK = High Molecular Weight Kininogen. PL = Phospholipid.

Fig. 1. The Classic Coagulation Cascade Model(6).

facilitate targeted therapy in a "medically" bleeding patient by providing information about platelet function and degree of fibrinolysis as well as factors produced in the liver. Standard coagulation tests and point-of-care tests will be discussed in detail with reference to their

Coagulation requires complex interactions of cellular and molecular components, mainly involving platelets, plasma and red blood cells. The process was classically described as a cascade of 'Intrinsic', 'Extrinsic', and 'Common' pathways (see Figure 1). These pathways

The Intrinsic Pathway is activated when FXII binds to exposed collagen of damaged endothelium. The cascade of activations occur as shown, and amplification also occurs (for example FXIIa converts prekallikrien to kallikrien and auto-activates more FXII). The resulting "Tenase" complex (shown in a dashed yellow line) activates FX. The Extrinsic Pathway is initiated by Tissue Factor, and results in a TF/FVIIa complex (in a dashed yellow line) that activates FX. The Common Pathway yields thrombin (FIIa), which not only activates Fibrinogen (FI) but also amplifies other stages of the cascade by activating FVIII, FV and FXIII. The ultimate result is a cross-linked Fibrin mesh. HMWK = High

individual utility in this group of patients.

Molecular Weight Kininogen. PL = Phospholipid. Fig. 1. The Classic Coagulation Cascade Model(6).

**2. Coagulation pathways** 

are useful in terms of interpreting some of the coagulation tests, but in vitro coagulation is less linear and occurs by a combination of these pathways. Current understanding of the coagulation process is best described by the cell-based model.

The coagulation factors were discovered in the 1940s and 1950s. They are proenzymes found in plasma, which are converted to active enzymes during the coagulation process. The factors were assigned roman numerals in the order they were discovered; each factor also has one or more names. The more commonly used ones are shown in the figure 2 (6). The numerals are prefixed by "F" for "factor", and the suffix "a" is used to indicate the activated form of the factor.


Fig. 2. Factor Numbers and Common name(s) – anomalies are shown in green
