The prothrombin time primarily assesses which coagulation pathway?

The prothrombin time primarily assesses which coagulation pathway?

• A. Intrinsic pathway
• B. Extrinsic pathway
• C. Common pathway
• D. Fibrinolysis

Answer: (B)

The main concept here is understanding what the prothrombin time (PT) tests in the coagulation cascade. PT uses tissue factor (thromboplastin) and calcium to trigger clotting, which primarily engages the extrinsic pathway by activating factor VII. Once VII is activated, it kicks off the rest of the pathway toward thrombin and fibrin formation, so PT is most sensitive to problems in this pathway (and to the common pathway factors that follow). In contrast, the intrinsic pathway is tested with the aPTT using a contact activator, and fibrinolysis is a separate process not measured by PT. That’s why the prothrombin time best reflects the extrinsic pathway.

The main concept here is understanding what the prothrombin time (PT) tests in the coagulation cascade. PT uses tissue factor (thromboplastin) and calcium to trigger clotting, which primarily engages the extrinsic pathway by activating factor VII. Once VII is activated, it kicks off the rest of the pathway toward thrombin and fibrin formation, so PT is most sensitive to problems in this pathway (and to the common pathway factors that follow). In contrast, the intrinsic pathway is tested with the aPTT using a contact activator, and fibrinolysis is a separate process not measured by PT. That’s why the prothrombin time best reflects the extrinsic pathway.