Which clotting factors does the PT measure?

The prothrombin time (PT) is a blood test that assesses the extrinsic and common pathways of coagulation. The correct answer involves factors that are specifically evaluated by this test.

The PT mainly measures the functionality of clotting factors that are part of the extrinsic pathway, primarily factor VII, which is vital for the initiation of the coagulation cascade in response to vascular injury. It also assesses factors that are involved in the common pathway, including factor II (prothrombin), which is critical for the conversion of fibrinogen to fibrin, and factor X, which is necessary for the formation of the prothrombinase complex that activates prothrombin.

Thus, the inclusion of factors 2, 7, 9, and 10 in the correct answer highlights the importance of factor VII aligning with PT testing, while factors II and X are crucial in the common pathway shared by both the intrinsic and extrinsic pathways. Factor IX is part of the intrinsic pathway but still can influence PT results indirectly through the common pathway.

Other options do not correctly align with what is measured by the PT. For instance, a combination of factors that do not include the critical extrinsic pathway contributors fails to represent the primary focus