Which pathways does prothrombin time (PT) evaluate in the coagulation cascade?

Prothrombin time (PT) specifically evaluates the extrinsic and common pathways of the coagulation cascade. The extrinsic pathway is initiated by tissue factor (thromboplastin) that is released at the site of injury, which then activates factor VII. This pathway leads to the activation of factor X, which is a crucial step that merges with the common pathway.

The common pathway involves factors X, V, prothrombin, and fibrinogen, ultimately leading to the conversion of prothrombin into thrombin, and then to the formation of a fibrin clot. The measurement of PT both assesses the integrity of the extrinsic pathway and provides insight into the functionality of the common pathway.

Understanding the specific roles of the coagulation pathways is critical in laboratory medicine practice, particularly in the clinical context of diagnosing bleeding disorders, monitoring anticoagulation therapy, and evaluating liver function.