Untitled Quiz

Blood Coagulation Tests

• Coagulation tests assess the blood's ability to clot (PT, PTT, BT)
• Hemostasis is the body's natural response to stop bleeding from an injured vessel.
• It involves a complex series of steps that lead to the formation of a blood clot.

What is Hemostasis?

• The integrity of blood vessels is crucial for proper blood transport to tissues.
• Hemostasis repairs injuries by forming a thrombus (blood clot) at the site of injury to prevent and stop blood loss.
• The term is derived from "hemo" (blood) and "stasis" (standing still).
• Blood vessel damage triggers hemostasis, which stops bleeding.

Hemostasis Stages

• Hemostasis occurs in two phases: primary and secondary.
• Primary hemostasis involves platelet activation and plug formation to control bleeding.
  • Vasoconstriction
  • Platelet adhesion
  • Platelet activation
  • Platelet aggregation/Platelet plug
• Secondary hemostasis involves the formation of a stable fibrin clot, solidifying the platelet plug.
  • The coagulation cascade which activates clotting factors following activation of clotting factors in blood plasma (extrinsic and intrinsic pathway, common pathway).

Hemostasis: Blood Clotting

• Serum is blood plasma minus its clotting proteins.
• Clotting (coagulation) factors are made by hepatocytes (liver cells), released into the bloodstream in an inactive form.
• Secondary hemostasis clotting is a series of steps culminating in the formation of insoluble fibrin threads from fibrinogen, forming a blood clot. This includes the extrinsic, intrinsic, and common pathways.
• Blood clotting prevents extensive bleeding when blood vessels are harmed.

Coagulation Tests (PT, PTT, and BT)

• Bleeding time (BT) assesses the primary hemostasis (platelets phase)
• Prothrombin time (PT) measures the extrinsic and common pathways function.
• Activated partial thromboplastin time (aPTT) measures the intrinsic and common pathways function.

Secondary Hemostasis

• Coagulation consists of the extrinsic, intrinsic, and common pathways. These pathways operate individually but converge.
• Extrinsic pathway starts with tissue damage and the release of tissue thromboplastin, activating Factor VII.
• Intrinsic pathway begins when exposed collagen activates Factor XII.
• Both pathways converge into the common pathway, which involves factors X, V, II (Prothrombin), I (Fibrinogen), and XIII.
• The final product is a stable fibrin clot.

Disorders of Primary Hemostasis

• Clinical signs include mucosal bleeding, hematuria, epistaxis, menorrhagia, and skin bleeds (petechiae, purpura, ecchymoses).
• Laboratory tests include platelet count and bleeding time.
• Disorders can be quantitative (low platelet count) or qualitative (platelets fail to function as expected). Examples include immune thrombocytopenic purpura (ITP)

Disorders of Secondary Hemostasis

• Clinical manifestations include deep tissue and joint bleeding, and re-bleeding after surgery.
• Laboratory evaluations include prothrombin time and activated partial thromboplastin time.
• Factor abnormalities (e.g., hemophilia A, hemophilia B, von Willebrand disease) are common causes.

Hemophilia A

• Factor VIII deficiency.
• Elevated aPTT, normal PT, normal platelet count, and bleeding time.

Hemophilia B

• Factor IX deficiency.
• Elevated aPTT, normal PT, normal platelet count, and bleeding time.

von Willebrand Disease

• Deficiency of von Willebrand factor (vWF).
• Prolonged bleeding time, normal PT, and increased aPTT.