Which test measures the intrinsic coagulation pathway?

Which test measures the intrinsic coagulation pathway?

• A. Bleeding Time Test
• B. INR Test
• C. Thrombin Time
• D. PTT Test

Answer: (D)

The test that evaluates the intrinsic coagulation pathway is the activated partial thromboplastin time (aPTT or PTT). In this assay, plasma is exposed to a contact activator and phospholipid in the presence of calcium, which starts the intrinsic cascade. The time it takes for a clot to form reflects how well the factors XII, XI, IX, and VIII, along with the subsequent common-pathway factors (X, V, II, fibrinogen), are functioning. If any of these intrinsic or downstream factors are deficient or inhibited, the clotting time lengthens. Bleeding time focuses on platelets and vessel integrity, not the coagulation cascade. The INR/PT measures the extrinsic pathway via tissue factor, so it’s not the intrinsic pathway. The thrombin time looks at the final step of converting fibrinogen to fibrin and can be affected by fibrinogen levels or thrombin inhibitors, rather than specifically assessing intrinsic versus extrinsic pathways.

The test that evaluates the intrinsic coagulation pathway is the activated partial thromboplastin time (aPTT or PTT). In this assay, plasma is exposed to a contact activator and phospholipid in the presence of calcium, which starts the intrinsic cascade. The time it takes for a clot to form reflects how well the factors XII, XI, IX, and VIII, along with the subsequent common-pathway factors (X, V, II, fibrinogen), are functioning. If any of these intrinsic or downstream factors are deficient or inhibited, the clotting time lengthens.

Bleeding time focuses on platelets and vessel integrity, not the coagulation cascade. The INR/PT measures the extrinsic pathway via tissue factor, so it’s not the intrinsic pathway. The thrombin time looks at the final step of converting fibrinogen to fibrin and can be affected by fibrinogen levels or thrombin inhibitors, rather than specifically assessing intrinsic versus extrinsic pathways.