Which test evaluates the intrinsic coagulation pathway?

Which test evaluates the intrinsic coagulation pathway?

• A. APTT
• B. PT
• C. Buccal mucosal bleeding time
• D. Thrombin time

Answer: (A)

The essential idea is distinguishing how the body's intrinsic coagulation cascade is measured versus other parts of the clotting system. Activated partial thromboplastin time specifically targets the intrinsic pathway by using an activation surface (such as kaolin) to trigger the intrinsic factors and then timing how long until a fibrin clot forms. Because it activates and tests the factors involved in the intrinsic cascade (plus the downstream common pathway), it’s the test that best reflects intrinsic pathway function. In contrast, the prothrombin time starts with tissue factor to evaluate the extrinsic pathway (and the common pathway), so it’s not the right measure of the intrinsic route. Buccal mucosal bleeding time assesses platelet function and vessel integrity, not the coagulation cascade. Thrombin time examines the final step of clot formation—the conversion of fibrinogen to fibrin—rather than the intrinsic pathway itself.

The essential idea is distinguishing how the body's intrinsic coagulation cascade is measured versus other parts of the clotting system. Activated partial thromboplastin time specifically targets the intrinsic pathway by using an activation surface (such as kaolin) to trigger the intrinsic factors and then timing how long until a fibrin clot forms. Because it activates and tests the factors involved in the intrinsic cascade (plus the downstream common pathway), it’s the test that best reflects intrinsic pathway function.

In contrast, the prothrombin time starts with tissue factor to evaluate the extrinsic pathway (and the common pathway), so it’s not the right measure of the intrinsic route. Buccal mucosal bleeding time assesses platelet function and vessel integrity, not the coagulation cascade. Thrombin time examines the final step of clot formation—the conversion of fibrinogen to fibrin—rather than the intrinsic pathway itself.