Which coagulation factors are involved in the common pathway of coagulation?

Coagulation Factors in the Common Pathway

The correct answer is A: factors X, V, II, and XIII are involved in the "common pathway" of coagulation.

Understanding the Coagulation Cascade

The coagulation cascade is traditionally divided into three pathways:

• Intrinsic pathway
• Extrinsic pathway
• Common pathway

According to the most recent guidelines from Praxis Medical Insights, the common pathway begins at the point of Factor X activation and includes the following sequence 1:

1. Factor X activation to Factor Xa
2. Factor Xa combines with Factor Va to form the prothrombinase complex
3. The prothrombinase complex converts prothrombin (Factor II) to thrombin (Factor IIa)
4. Thrombin converts fibrinogen to fibrin
5. Factor XIII is activated to Factor XIIIa, which cross-links fibrin strands

This clearly establishes that factors X, V, II, and XIII are the components of the common pathway 1.

Evidence Supporting This Classification

The common pathway represents the final convergence point where both the intrinsic and extrinsic pathways meet. As stated in the Journal of Extracellular Vesicles, "Both the intrinsic and extrinsic pathways converge into a final common pathway. In the common pathway, factor X is activated into factor Xa, and factors Xa and factor Va together form the prothrombinase complex, which catalyses thrombin formation (IIa) from prothrombin (II)" 2.

Additionally, Blood Coagulation Factor X is described as sitting "at a pivotal point in the coagulation cascade and has a role in each of the three major pathways (intrinsic, extrinsic and the common pathway)" 3.

Why the Other Options Are Incorrect

• Option B (factors IX, VIII, II, and I): Factors IX and VIII are part of the intrinsic pathway, not the common pathway. They form the intrinsic tenase complex that activates Factor X 1.

• Option C (factors VII, V, II, and I): Factor VII is part of the extrinsic pathway, forming the extrinsic tenase complex with tissue factor 1.

• Option D (factors XI, XI, VIII, and IX): These factors are all part of the intrinsic pathway and are involved in the sequence: XII → XIIa → XI → XIa → IX → IXa, which forms the intrinsic tenase complex with Factor VIIIa 1.

Clinical Relevance

Understanding the common pathway is crucial because:

• Many anticoagulant medications target factors in the common pathway
• Factor X is a central therapeutic target due to its pivotal position in the coagulation cascade 3
• Deficiencies in common pathway factors can lead to significant bleeding disorders
• The common pathway requires calcium ions (Ca²⁺) for many reactions, which is why anticoagulants like citrate work by chelating calcium 1

Key Points to Remember

• The common pathway begins with Factor X activation
• Factors X, V, II, and XIII are the key components of the common pathway
• The common pathway results in the formation of cross-linked fibrin, the final product of coagulation
• The common pathway occurs primarily on cell surfaces (particularly activated platelets), not freely in plasma 1