This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Clotting factor, Subject name: Pathology
Marker for intrinsic pathway is: 
Select and explain. 
A. Prothrombin Time (PT), B. Bleeding time (BT), C. Clotting time (CT), D. Activated paial thromboplastin time (aPTT)
D: Activated paial thromboplastin time (aPTT)
Answer: D: Activated paial thromboplastin time (aPTT) 
Explanation: 1.The Activated paial thromboplastin time (PTT) assay screens the function of the proteins in the intrinsic pathway (factors XII, XI, IX, VIII, X, V, II, and fibrinogen). 2. Prothrombin time - Assay assesses the function of the proteins in the extrinsic pathway (factors VII, X, V, II, and fibrinogen). 3.Bleeding time - It indicates the functioning of the platelets. 4.Clotting time - It is altered in the patients who are having either a defect in the platelets or there is a defect in the clotting factors.