Chapter 4 - Hemostasis and related disorders Flashcards
What are the four steps of hemostasis?
1. Vasoconstricion transient
2. Adhesion
3. Degranulation shape change, and release of mediators.
4. Aggregation
Which mediators mediate which of the four steps of hemostasis?
- Vasoconstriction: reflex neural stimulation (knee-jerk) and endothelin.
- Adhesion: Von Willebrand factor (sub.endo.coll.) and GPIb vWf til platelet.
- Degranulation: ADP (GPIIb/IIIa exposure), TXA2 (aggregation, from COX)
- Aggregation: GPIIb/IIIa + fibrinogen links platelets.
Case: Patient presents with recurrent nosebleeds that last for a very long time.
On blood smear you find indications of a slightly low platelet count, but the ones present are quite large.
Which hemostatic mediator is most likely deficent?
Bernard-Soulier syndrome
Decreased GpIb leads to platelet to vWF adhesion.
Case: 10 year old boy fell of his bicycle, and sustained minor cuts and bruises. His mother took him to the emergency services when he would not stop bleeding. He has no history of increased bleeding time, and is healthy except for a viral infection a few days ago.
What should be the initial treatment?
Immune thrombocytopenia
Corticosteriods and IVIG
Autoimmune production of IgG against platelets causes thrombocytopenia in children or adults. IVIG may be used to treat symptomatic bleeding, and splenectomy is performed in refractory cases.
Case: Patient presents with recurrent nosebleeds that last for a very long time.
On blood smear you find indications of a normal platelet count, but there is no platelet clumping.
Which hemostatic mediator is most likely deficent?
Glanzman thrombasthenia
GpIIb/IIIa is deficent. It uses fibrinogen to link together platelets. Deficency causes a platelet plug formation.
Case: 35 year old female presents with symptoms of a low platelet count, increased bleeding time, fever and neurological symptoms. You find schistocytes on the blood smear examination. What is the most likely cause of the symptoms.
Thrombotic thrombocytopenia Purpura
An autoantibody aganst ADAMTS13 (cleaves vWF multimers) leads to increased formation of microthrombi and depletion of the platelet pool. When the red blood cells cross the thrombi they are damaged and therefore show as schistocytes (helmet cells)
Case: 14 year old female presents with acute renal failure and diaorrhea. She has a low platelet count, increased bleeding time and you find schistocytes on the blood smear examination. What is the most likely cause of the symptoms.
Hemolytic-uremic syndrome
Commonly caused by shiga toxin producing E.coli. The toxin damages endothelial cells which creates microthrombi. This depleates the platelet pool and damages the RBCs.
What are the normal lab findings of Microangiopathic Hemolytic Anemia?
1. Thrombocytopenia with increased bleeding time.
2. Normal PT/PTT
3. Anemia with Schistocytes
4. Increased Megacaryocytes in the bone marrow.
Which factors can be tested with a PTT test?
XII, XI, IX, VIII, V, II and I. (intrnsic + common pathway)
Which factors can be tested with a PT test?
VII, V, II, I. (Extrinsic + common pathway)
What is the common clinical bleeding difference between Primory and Secondary hemostasis disorders?
Primary: Mucosal and skin bleeding caused by not being able to produce a basic plug.
Secondary: Deep tissue and re-bleeding caused by not being able to maintain a plug.
Which factors activate the extrinsic, intrinsic, and common coagulation pathways?
Extrinsic: Tissue Thromboplastin (two letters = PT)
Intrinsic: Subendothelial Collagen (three letters = PTT)
Common: Factor X
Which test should you do to differentiate between Hemophilia A/B
Test for FVIII and FIX.
How can you differentiate between coagulation factor deficency and coagulation factor inhibitor?
Mixing test
When you mix in normal plasma with the patients plasma you are adding more coagulation factors. In a deficency this will correct the PTT/PT, while in a inhibitor situation it will not cause any change.
Case: Newborn baby refugee presents with neonatal bleeding disorders. There has been no post natal care. Which deficency usually treated in post natal care may be the source of the disorder?
Vitamin K
It causes a general coagulation defect (II, VII, IX, X, protein C, and protein S)
