Flashcards in Hemostasis Deck (76)
What are the four overlapping phases of the hemostatic process?
Primary hemostasis, Secondary hemostasis, Clot limitation, and Clot dissolution.
Describe primary hemostasis.
Local vasoconstriction and formation of a loose platelet plug.
Describe secondary hemostasis.
Circulating coagulation factors, via the clotting cascade, form fibrin that stabilizes the platelet plug.
What are the four steps in the formation of a platelet plug?
Adhesion, activation, aggregation, and thrombin activation.
Which bleeding syndrome is associated with a deficiency of GP1b and how does this present clinically?
Bernard-Soulier syndrome. Platelets bind poorly to vWF, which results in bleeding gums, significant bleeding with small injuries, and profuse bleeding with menses.
Which bleeding syndrome is associated with a deficiency of the GP2b/3a platelet complex and what is the associated defect?
Glanzmann Thrombasthenia. Patients are unable to aggregate platelets.
How does Clopidogrel affect platelet function?
It blocks the ADP effects on the platelets, which normally works to induce more platelet activation and thrombogenesis.
What is the presumed factor underlying Prinzmetal angina and how does it work?
Thromboxane A2 has vasoconstrictive properties and is the presumed underlying cause of Prinzmetal angina.
During which step in platelet plug formation is the clotting pathway activated?
The clotting pathway is activated during step 3 of the platelet plug formation process - aggregation.
Which clotting factors are involved in the intrinsic pathway?
Factors 8, 9, 11, and 12
Which clotting factors are involved in the extrinsic pathway?
The 7a-tissue factor complex comprises the extrinsic pathway.
Which clotting factor is involved in both the intrinsic and extrinsic pathways?
Both pathways converge to activate Factor 10.
Name 4 important hemostatic functions carried out by thrombin.
Thrombin is critical in the conversion of fibrinogen to fibrin in the platelet plug, in activating Factor 13 (the resulting Factor 13a interacts with fibrin to make a covalently bonded, stabilized, cross-linked fibrin clot), in stimulating self-regeneration by activating Factors 5, 8, and 11, and in activating platelets as part of primary hemostasis.
Describe the process by which clot size is limited.
Clot size limitation occurs because thrombin modulates its own production by combining with an endothelial cell surface protein (thrombomodulin) to activate Protein C. Activated Protein C, combined with Protein S, deactivates Factors 5a and 8a, thereby limiting thrombin production.
Describe the process by which clots are dissolved.
Clot dissolution (fibrinolysis) is initiated by tissue plasminogen activator (tPA) released from endothelial cells. tPA catalyzes the conversion of plasminogen to plasmin, which breaks down fibrin and fibrinogen and dissolves the clot.
What would you expect to see clinically in a patient with Protein C or Protein S deficiency?
Thrombotic tendency. These patients would present with clots, such as DVTs.
At the bedside, how can you differentiate between a primary hemostatic problem and a coagulation problem?
Primary hemostatic problems result in multiple, tiny, superficial hemorrhages (petechiae, ecchymoses, and mucocutaneous bleeding), while coagulation disorders present with deep tissue bleeding such as hematomas and hemarthroses.
Which 5 tests are commonly done in the initial evaluation of a bleeding disorder?
PT, PTT, thrombin time, platelet count, and bleeding time (or rapid platelet function analysis (PFA)).
What does prothrombin time (PT) measure?
Prothrombin time measures the function of the extrinsic and common coagulation pathways (think Factor 7).
What does activated partial thromboplastin time (PTT) measure?
PTT measures the function of the intrinsic and common coagulation pathways (Factors 8, 9, 11, 12).
What does the thrombin time measure?
Thrombin time measures the time of conversion of fibrinogen to fibrin.
What would an increased thrombin time indicate?
An increased thrombin time reflects decreased or defective fibrinogen, elevated fibrin degradation products, or the presence of heparin or heparin-like anticoagulants.
What are bleeding time and rapid platelet function analysis testing used to assess?
These tests reflect the effectiveness of platelet aggregation, and are used to determine the adequacy of platelet number and function.
A deficiency in which clotting factor does not result in a bleeding disorder?
What does a mixing study show?
A mixing study is when a patient's plasma is mixed 1:1 with normal plasma. If the PTT corrects following mixing, the patient has a clotting factor deficiency. If it does not correct, the patient has developed an inhibitor to a clotting factor protein (usually a lupus anticoagulant or Factor 8 inhibitor).
What does it mean if the PTT is prolonged but the PT is normal?
There is either a clotting factor deficiency or a circulating clotting factor inhibitor.
What does it mean if the PT is prolonged but the PTT is normal?
Factor 7 deficiency, mild liver disease, mild Vitamin K deficiency, or therapeutic Warfarin levels.
Know Figure 24-7 and Table 24-6 ***
Which clotting factor is low in children with hemophilia A?