Which reagents are used in the PT test?

The prothrombin time (PT) test is designed to assess the function of the extrinsic pathway of coagulation and is mainly used to evaluate the presence of clotting factors (primarily factors I, II, V, VII, and X) involved in the coagulation cascade.

The correct choice, which includes thromboplastin and calcium, highlights the essential components used in this test. Thromboplastin, which is a mixture of tissue factor and phospholipids, serves to activate the extrinsic pathway of coagulation when added to the patient's plasma. This activation initiates the cascade leading to the formation of a fibrin clot. Calcium, on the other hand, is critical because it is a vital cofactor necessary for the coagulation cascade to occur; it facilitates various steps in the conversion of prothrombin to thrombin, ultimately leading to clot formation.

The combination of these two reagents allows for the proper assessment of the coagulation process, making them indispensable for the PT test.