Hemostasis and Coagulation Cascade

Which coagulation parameter best distinguishes Disseminated Intravascular Coagulation (DIC) from Vitamin K deficiency in a critically ill patient with prolonged PT and aPTT?

In the intrinsic pathway of coagulation, which factor acts as the cofactor for Factor IXa to form the tenase complex?

A 58-year-old man with advanced pancreatic cancer presents with acute onset of bleeding from multiple sites (gum bleeding, hematuria, melena). His wife reports he was well 2 days ago. Physical examination reveals petechiae, ecchymoses, and hepatomegaly. Laboratory results: Hemoglobin 7.8 g/dL, Platelet count 32,000/μL, PT 28 sec (control 12 sec), aPTT 58 sec (control 32 sec), Fibrinogen 0.8 g/L (normal 2–4 g/L), D-dimer 8.5 μg/mL (normal <0.5 μg/mL), Prothrombin time ratio (INR) 2.3. Peripheral blood smear shows schistocytes. What is the primary mechanism of coagulation abnormality in this patient?

A 28-year-old man with a family history of bleeding disorders presents with spontaneous hemarthrosis and muscle hematomas. Prothrombin time (PT) is normal, but activated partial thromboplastin time (aPTT) is prolonged. Platelet count and bleeding time are normal. Which investigation is most appropriate to confirm the diagnosis?

A 32-year-old woman presents to the emergency department with spontaneous bleeding from gums, epistaxis, and petechial rash over lower limbs for 2 days. Platelet count is 8,000/μL. Coagulation profile (PT, aPTT, fibrinogen) is normal. Peripheral blood smear shows no schistocytes. What is the most appropriate immediate next step in management?