Which laboratory test assesses the intrinsic pathway of coagulation?

The activated partial thromboplastin time (aPTT) test is specifically designed to evaluate the intrinsic pathway of coagulation. This pathway involves various clotting factors, primarily factors VIII, IX, XI, and XII, which are crucial for the formation of blood clots. When aPTT is performed, the test measures the time it takes for blood to clot after specific reagents are added that activate the intrinsic pathway.

In clinical settings, aPTT is often used to monitor patients who are on anticoagulation therapy, particularly those receiving unfractionated heparin. This makes aPTT a vital tool in assessing bleeding risks and in guiding treatment regarding coagulation disorders.

In contrast, the prothrombin time (PT) measures the extrinsic pathway of coagulation, which involves factors I, II, V, VII, and X. The complete blood count (CBC) assesses overall blood components without focusing specifically on coagulation pathways. The fibrinogen test determines the level of fibrinogen in the blood but does not specifically assess the intrinsic pathway of coagulation. Thus, the correct answer clearly identifies the test that focuses on the intrinsic pathway.