What is the definition of hemostasis and what are the general overarching steps?
Hemostasis: process that prevents blood loss from damaged blood vessels
Adhesion, activation and cohesion of platelets (platelet plug)
Clot stabilization by fibrin
What are some important receptors on platelets?
GPIbalpha von Willebrand Factor/Adhesion
What types of granules are in platelets?
What do Dense Granules contain?
What do Alpha Granules contain?
Dense: ADP, ATP, Serotonin, Ca2+
(ADP and ATP receptors are also on platelets)
Coagulation proteins: F-v, Fibrinogen/vWF
Platelet factor 4
What are activating substrates for platelets?
What are their respective receptors?
What intracellular signaling goes on?
What actions are a result of activation?
Gq, PLCbeta increasing IP3 and DAG
Integrin activation/Granule secretion/Cytoskeletal rearrangements (shape change)
Steps of platelet adhesion?
Arterial thrombosis: injury of blood vessel wall
Venous thrombosis: altered blood flow/hypercoagulability
What are the steps to platelet adhesion?
Damage exposes collagen
von Willebrand factor in plasma sticks to collagen and becomes activated, expressing domains GPIb and GPIIb/IIIa
Platelets GPIb receptors bind vWF
Platets release granules, activating other platelets (free, not adhesed to epithelium)
Membrane procoagulant expression leading to thrombin and clot (more phosphatidylserine)
Platelet cohesion via fibrinogen bridges (activated platelets activate fibrinogen receptors which is constitutively in the plasma phase)
Result: primary platelet plug. But not stable (so requires coagulation)
What is cell based coagulation?
Series of transformations of proenzymes to activated enzymes resulting in formation of thrombin (IIa) driving fibrin clot formation.
What are the steps to cell based coagulation?
I. Initiation: Tissue factor/VIIa activate factor IXa and Xa
II. Amplification: Initial thrombin activation Va, VIIIa, XIa, and platelets
III. Propagation: XIa augments process by driving further IXa formation. IXa catalyzes further thrombin formation on platelets
IV. Thrombin drives transformation of fibrinogen to fibrin and crosslinking
What are the vitamin K dependent proteins?
Why do they require Ca2+ for action?
2, 7, 9, 10 (pro-coagulant)
Protein C and S (anticoagulant)
These contain alpha-glutamic acids that are carboxylated, negatively charged able to sit down on membranes through mechanism involving Ca2+ ions to neutralize the negative charge).
What type of protein is Thrombin
What is it's mechanism?
Is it stable at this point?
Thrombin is a protease
Binds to fibrinogen and cleaves fibrinopeptides, generating fibrin monomers consisting of one E domain and two D domains. Adjacent monomers self-assemble.
Not stable. Needs factor 13 (which is activated by thrombin) which makes peptide bonds to crosslink polymerizations covalently
Compare and contrast PT vs. PTT
PTT/surface factors/XI, IX/Intrinsic (deficiency can be asymptomatic because not important for systemic coagulation
What is the fibrinolytic system comprised of?
Each of their actions?
t-PA, Plasminogen, alpha2-antiplasmin, D-dimer
t-PA-Activates plasminogen to plasmin
Plasminogen activates to plasmin, which degrades fibrin clots (main targeT) as well as factors VIII, V
Alpha2 antiplasmin-degrades plasmin
How does inflammation and injury favor thrombosis?
Inflammation: tissue factor
Injury: exposed collagen
How is thrombosis inhibited?
PGI2, NO are normally released from endothelial cells to prevent clots
Thrombomodulin system (Protein C system to degrade coagulation factors and when thrombin bound acts as an anticoagulant)
Immune thrombocytopenia Purpura
How does the blood film appear?
What types are there and what are important details of each?
Blood film: RBC and WBC normal. Large platelets
There are 2 types, childhood and Adult
Childhood: abrupt onset with severe thrombocytopenia with antecedent viral syndrome common. Mechanism of autoab to platelet surface glycoproteins. Most patients recover
Adult: Onset insidious with minor bleeding and no antecedent viral illness. Decreased paltelet survival with decreased production. Only 5% survive spontaneously
Treatment: steroids/immunoglob/antiCD20 Rituxumab/Platelet growth factors
What is Heparin induced thrombocytopenia?
How to dx?
What are characteristics?
Platelet factor 4 interacts with heparin, autoantibodies to this complex form. These antibodies also bind to surface of platelets and activates them. Thus moderate thrombocytopenia and thrombotic events.
Dx: Lab confirm PF4-Heparin ELISA or SRA (a paltelet function assay)
4Ts: Thrombocytopenia, timing, thrombosis, no oTher causes
Treatment: Stop heparin and begin alternative anticoagulant such as direct thrombin inhibitor (DTI) argatroban, bivalirudin
Thrombotic Thrombocytopenic Purpura
What is it
What are required parts of diagnosis?
Other parts of diagnosis?
Mechanism of pathogenesis
Idiopathic autoab to ADAMTS13 protein
Hemolytic uremic syndrome (shiga toxin associated HUS)
Dx: Required: Microangiopathic hemolytic anemia and thrombocytopenia
also but not required for dx: Renal failure, mental status change, fever
Need to rule out other dx.
ADAMTS13=enzyme regulator of vWF/platelet interactions. Dysfunction results in failed cleavage of vWF causing string of platelets, breaking off and embolizing.
What is PFA-100?
How does it work?
How do you use the results of this test in diagnosis?
Membrane coated with collagen with holes.
Screens for platelet and vWF function through measured aperture closure time. Not very specific thugh so if no suspicion and normal aperture closure time-->stop
However if prolonged or high suspicion, then go ahead with tests of von Willebrand factor. If normal still then check platelets.
What are functions of von Willebrand factor?
Support platelet adhesion to exposed collagen
Carrier for factor VIII (so maintains it in circulation. Thus abn vWF may lead to FvIII deficiency [long PTT]
How can you evaluate vWF?
Ristocetin cofactor assay (activates vWF like collagen)
What are types of platelet dysfunction?
Congenital absence of
GPIb: Bernard Soulier syndrome
How is Prothrombin time measured?
Tissue factor, phospholipid ca2+ added to citrated plasma and clotting time measured
Reported in seconds and INR
INR=(patient PT time/Mean normal prothrombin time)^ISI
Monitors vit k antagonism from Warfarin
How is PTT measured?
What can make it prolonged?
Surface activators, phospholipid, ca2+ added to citreated plasma
Prolonged if missing IX or VIII (hemophilia)
What is a 1:1 mix
Mix patient plasma with nromal containing 100% of all factors.
If clotting time is normal, then factor deficiency likely
If clotting time remains prolonged, inhibitor is likely
Differential dx for Long PTT w normal PT
Factor def: VIII, IX, XI, XII
vWD if VIII low.
Inhib: heparin, lupus anticoag, specific factor inhibition
Differential dx for Long PT
Factor deffic: Factor VII, combination of factor deficiency from Vit K deficiency/oral anticoag/liver disease
Inhib: Factor inhibition, lupus inhibition (rare)
Diferential dx for Long pt AND long PTT
Factor def isolated: X, V, II, fibrinogen
Multiple factor def: liver disease if severe, vit k defic if severe, DIC
Inhib: Isolated factor inhib of X, V, II
drugs: heparin, direct thrombin inhibitors, lupus inhibitor, inhibition of fibrin polymerization