Hematology - Hemostasis Flashcards
Coagulation Platelet Activation Hypercoagulable States Coagulopathies Platelet Disorders Antiplatelet Drugs Anticoagulant Drugs
how does the body prevent blood loss when there is damage to a blood vessel?
thrombus formation
platelets are activated and fibrin crosslinks to form a clot
what is the first line of defense against bleeding?
vasoconstriction in response to endothelial damage
mediated by ENDOTHELINS
what are endothelins?
key mediator in the vasoconstrictor compensatory response to prevent blood loss
they are proteins
they are potent vasoconstrictors
they are released by endothelial cells near the damage
what are endothelin receptor blockers used for?
Pulmonary HTN
what are coagulation factors?
proteins synthesized by the liver
soluble in plasma
activated when endothelial damage occurs
forms fibrin => fibrin mesh => blood clot
what form do coagulation factors circulate in?
zymogens
what are serine proteases?
protein cleavage enzyme that contains serine
clotting factors can activate into a serine protease
what are the steps in the clotting cascade?
activation of what clotting factor will lead to fibrin formation?
X –> Xa
what drugs act on the clotting cascade?
what is the positive feedback associated with thrombin?
factor IIa activates factors V, XI, VIII
XIa activates IX —> IXa
IXa + VIIIa —> Xa
what activates factor X in the setting of endothelial damage?
tissue factor becomes activated by endothelial damage which interacts with factor VII to activate factor X
TF:VIIa complex activates Xa
what is tissue factor?
aka thromboplastin
glycoprotein expressed in SUBendothelial cells NOT endothelial cells => no contact with citculating blood unless exposed by endothelial damage
what is thrombin?
aka factor IIa
prothrombin is factor II
can activate factors V, XI, VIII
what are the components of extrinsic Xase?
phospholipid: TF-bearing cells
Enzyme: factor VIIa
co-factor: TF
substrate: factor X
what are the unique features of factor VIII?
produced in endothelial cells, not in the liver
circulates bound to vWF
released from vWF in response to vascular injury
what are the components of intrinsic Xase?
phospholipid: platelets
enzyme: factor IXa
co-factor: factor VIII (VIIIa)
substrate: factor X
what is vWF?
von willebrand factor
critical for platelet aggregation
binding to vWF increases VIII plasma half life
what cells produce vWF?
endothelial cells and megakaryocytes
what are the multicomponent complexes that activate X –> Xa?
- Extrinsic Xase
- Intrinsic Xase
what is calciums role in coagulation?
used to be called factor IV - required for the clotting cascade
activated platelets release calcium
EDTA binds calcium in blood samples and prevents clotting
what is the order of the intrinsic pathway?
XII
XI
IX
X
II
I
what is the order of the extrinsic pathway?
TF:VIIa
X
II
I
what is factor XIII’s job?
crosslink fibrin to stabilize plug
requires calcium as a co-factor
what activates factor XIII?
thrombin (IIa)
what happens in the absence of factor XIII?
inadequate clot formation
what is factor XII?
aka Hageman factor
used for PTT test
activted by contact with negative charges (silica)
what can activate factor XI?
thrombin and factor XII
what is PTT?
partial thromboplatin time
tests the intrinsic pathway
how does the PTT test work?
plasma is added to negatively charged substance, usually silica
measure how long it takes for a clot to form
tests intrinsic pathway
what is the PT test?
prothrombin time
add plasma to TF and measure how long it takes for a clot to form
tests extrinsic pathway
what does the intrinsic pathway require to function normally?
kinins
how does factor XII produce bradykinin?
activates PK –> Kallikrein
HMWK —–> bradykinin
what activates the intrinsic pathway?
factor XII - aka the contact pathway because it becomes activated with contact to negatively charged substances
what are kinins?
peptide hormones/signaling molecules that link coagulation with inflammation
what do kinins circulate as and what activates them?
kininogens activated by kallikreins
what is bradykinin?
vasodilator
increases vascular permeability
can cause pain
what is bradykinin degraded. by?
ACE and C1 inhibitor protein
what happens to [bradykinin] with ACE inhibitors?
bradykinin levels increase
can cause angioedema
hereditary angioedema
C1 inhibitor protein deficiency
what does factor XII do?
activates clotting and produces bradykinin
what is prekallikrein deficiency?
rare condition that results in a markedly long PTT
factor XII an not activate normally
no bleeding problems bc the physiologic significance of factor XII is unkown
what is the relationship between protein C and S?
APC requires protein S as a co-factor
what are the important, naturally occurring, deactivators of coagulation?
antithrombin III
protein C & S
TF pathway inhibitor
what is antithrombin III?
a serpin - inhibts serine proteases
produced by the liver
what activates antithrombin III?
endothelium - endothelium makes heparan sulfate molecules that activate antithrombin
*basis for role of heparin drug therapy
antithrombin III deficiency
hypercoagulable state
what are the serine proteases?
factors II, VII, IX, X, XI, XII
What are proteins C and S?
glycoproteins synthesized in the liver
protein C: zymogen
active = APC (activated protein C)
what does APC do?
inactivates factors Va and VIIIa
what activates protein C?
thrombomodulin
what is thrombomodulin?
cell membrane protein found on endothelial cells
binds thrombin => complex activates protein C
what is protein S?
co-factor for APC to inactivate factors Va and VIIIa
circulates in active form so it can bind APC
how does protein C do its job?
thrombomodulin:thrombin complex activates protein C (APC)
when endothelium is healthy, it produces a lot of thrombomodulin which binds thrombin to activate protein C
what are steps for protein C to inactivate factors Va and VIIIa?
thrombomodulin binds thrombin
complex activates protein C (APC)
circulating Protein S binds APC
inactivation
what is the tissue factor pathway inhibitor?
TFPI
inactivates Xa
what are the 2 domains of fibrinogen and how are the involved in crosslinking fibrin?
E - central
D - side
factor XIII crosslinks fibrin and creates E linked to 2 D’s
plasmin breaks down fibrin into FDP’s and D-dimers
how does TFPI inactivate Xa?
- directly binds Xa —> deactivated
- binds TF/VIIa complex —> prevents X activation
what drug causes levels of TFPI to increase?
heparin - may contribute to antithrombic effect
once the clot is formed, what breaks it down?
plasminogen and plasmin
what is plasminogen
zymogen synthesized by liver
active form = plasmin
what does plasmin do?
breakdown fibrin (main job)
broad substrate specificity
also degreades clotting factors and fibrinogen
what are the naturally occurring plasminogen activators?
tPA and urokinase
streptokinase
what do tPA and urokinase do?
synthesized by endothelial ells, actiivate plasminogen to plasmin and clean up any fibrin that formed inside blood vessels
what plasminogen activtors can be used in the treatment of acute MI and stroke?
tPA
urokinase
streptokinase
streptokinase
streptococcal protein activates plaminogen
what are the breakdown products of fibrin?
FDPs and D-dimers
what are D-dimers?
special type of FDP
presence indicates clot breakdown
what Dx can an elevated D-dimer indicate?
DVT/PE
what is the only way to get D-dimers?
breakdown of CROSSLINKED fibrin from factor XIII
What do FDPs indicate?
plasmin activity
plasmin can directly convert fibrin into FDPs without clot formation
what is plasmin fibrinolysis?
overactive plasmin
increased FDPs; normal D-dimer****
what happens to result in plasmin fibrinolysis?
aka hyperfibrinolysis
plasmin breakdown of fibrinogen - not fibrin - forms FDPs
plasmin can deplete clotting factors
why are D-dimers normal (0) in primary fibrinolysis?
no clot or crosslinked fibrin = no D-dimers
what will PT/PTT show in primary fibrinolysis?
increased with bleeding
similar to DIC
why is prostate cancer a risk factor for primary fibrinolysis?
cancer cells release urokinase
how can cirrhosis lead to primary fibrinolysis?
loss of α-2 antiplasmin from liver causing overactive plasmin
FDPs & D-dimers key points
clot breakdown - increased FDPs & D-dimers
hyperfibrinolysis - increased FDPs w/ normal D-dimer
increased D-dimer used to Dx thrombotic disorders
elevated levels of D-dimer seen in DVT/PE - sensitive, not specific
what are the vitamin K dependent clotting factors?
II
VII
IX
X
protein C
protein S
vitamin K deficiency
bleeding
what drug is a vitamin K antagonist?
warfarin
what is ESR?
erythrocyte sedimentation rate
the rate of RBC sedimentation in test tube
increased in inflammatory conditions
what is normal ESR?
men = 0-22 mm/hr
women = 0-29 mm/hr
why is ESR increased in inflammatory conditions?
during inflammation, protein levels in the plasma increase –> the proteins are sticky and cause the RBCs to clump together
the clumps will settle faster
acute phase reactants
serum proteins tht rise in inflammation or tissue injury
driven by cytokines
synthesized in liver
what are the proteins in plasma that cause ESR to increase in inflammatory conditions?
acute phase reactants:
fibrinogen
ferritin
CRP
what does CRP do?
binds bacteria and activates complement
where do platelets come from? how long do they live?
megakaryocytes
8-10 days
what regulates platelet production?
thrombopoietin (TPO)
what is thrombopoietin?
glycoprotein produced mainly in the liver
what do platelets do?
aid in hemostasis after vascular injury
activated platelets seal damaged vessels
platelets circulate in their inactive form, what activates them?
endothelial injury
stimuli from other activted platelets
describe the steps in making a platelet plug
- adhesion to sub-endothelium
- aggregation - platelet-platelet binding
- secretion - release of granule contents
what is Von Willebrand factor?
- a large glycoprotein that is synthesized by endotheial cells and megakaryocytes
- present in platelets
- some found in plasma
- released on vascular injury
where is vWF stored?
Weibel-Palade bodies in endothelial cells
alpha granules in platelets
when is vWF released?
on vascular injury activated platelets degranulate and endothelial cells release vWF
what are Weibel-Palade bodies?
where platelets are stored in endothelial cells
releases vWF and P-selectin
what are the 3 main roles of vWF?
- carrier protein for factor VIII
- binds platelets to damaged endothelium
- binds activated platelets together (aggregation)
when is factor VIII released?
in the presence of thrombin (VIIIa)
what are membrane glycoproteins?
amino acid and glucose molecules
on the surface of platelets
interact with other structures/molecules
what are the membrane glycoproteins important for hemostasis?
GPIb, GPIIb/IIIa
what happens during platelet adhesion?
vascular damage = exposure to sub-endothelial collagen –> binds vWF
once vWF is bound to the sub-endothelial collagen, it can then bind the GPIb R on patelets
what happens during platelet aggregation?
GPIIb/IIIa changes confromation when platelets are activated
what is the most abundant surface R on platelets?
GPIIb/IIIa
what is inside out signaling?
refers to the process of platelet aggregation where cell activity (platelet activation) leads to an altered R
GPIIb/IIIa R will not bind unless platelets are activated
usually the R is altered then some cell activity is triggered
what can activated GPIIb/IIIa R bind to?
fibrinogen or vWF
what happens after GPIIb/IIIa is activated?
binds fibrinogen or vWF which allows for platelet aggregation
how do platelets aggregate?
uses fibrinogen or vWF as a link between platelets, connects platelets together by their GPIIb/IIIa R’s
what are the 2 ways platelets can be activated?
binding to subendothelial collagen
stimulation by activating substances released from other platelets
what happens during platelet secretion?
when one platelet is activated it will release its stored contents which can then go and activate other platelets
this is how the activation of 1 platelet can lead to the activation of many others
what are the platelet granules?
alpha granules (most abundant)
&
dense granules
what are contained in alpha granules?
fibrinogen
vWF
platelet factor 4
what are the contents of dense granules?
ADP
Calcium
Serotonin
what is platelet factor 4?
PF4
released from alpha granules, binds to endothelial cells
what is the role of PF4 in heparin induced thrombocytopenia?
antibodies formed to PF4 complexed with heparin
antibodies bind PF4-heparin –> platelet activation
=> diffuse thrombosis
=> low platelets from consumption
life threatening S/E of heparin
what is the role of serotonin in platelet activation?
stored in dense granules, released on platelet activation
basis for serotonin release assay
what is the serotoning release assay?
screening test for HIT
donor patelets radiolabeled with radioactive serotonin
patient serum (person screening for HIT) and heparin added
if HIT antibodies are present, excessive serotonin will be released from the donor platelets
what is the role of ADP in platelet activation?
stored in dense granules
released by RBCs when damaged
binds to 2 GPCR’s - P2Y1 & P2Y12
when ADP binds to P2Y1 or P2Y12 what happens?
decreased cAMP inside of platelets leading to platelet activation
what class of anti-platelet drugs increase cAMP?
phosphodiesterase inhibitors
how do phosphodiesterase inhibitors work?
increase in cAMP inside of platelets blocks activation
ADP binds P2Y1
calcium is released
change in platelet shape
ADP binds P2Y12
platelet degranulation => increased aggregation
what do P2Y12 receptor blocking drugs do?
what are they?
“ADP R blockers”
inhibit platelet activity
clopidogrel
prasugrel
ticlopidine
ticagrelor
what is TXA2?
thromboxane A2
powerful platelet activator
TXA2 R found on platelets
basis for aspirin therapy
what is TXA2 derived from?
lipids in cell membranes
what does aspirin block?
TXA2 formation
what does phospholipase A2 do?
enzyme that takes lipids from the cell membrane and converts them into arachadonic acid
what is an INR?
international normalized ratio
where is arachadonic acid released?
sites of vascular injury
also stored in platelets
aracadonic acid —> TXA2
converted by platelets with the enzyme cyclooxygenase (COX)
TXA2 is then released by platelets to activate more platelets
MOA of aspirin?
inhibits COX –> decreased TXA2 –> platelet activation
what is bleeding time? how is it performed?
test of platelet function
small cut to patients arm –> filter paper applied/removed until bleeding stops –> record time
rarely done in modern era
prolonged bleeding time
platelet function problem
what are coagulopathies?
bleeding disorder within the clotting cascade
what bleeding disorders have an abnormality of the coagulation cascade?
hemophilia
vitamin K deficiency
how are bleeding disorders classified?
abnormal coagulatin cascase
abnormal platelets
mixed disorers
what bleeding disorders have abnormal platelets?
Bernard-Soulier
Glanzmann’s thrombasthenia
ITP; TTP
uremia
what bleeding disorders are mixed?
Von Willebrand disease
DIC
liver disease
normal PT
~10s
what is thrombin time?
add thrombin to samlpe and record time to form clot
the only way this test will be abnormal is if there is a thrombin inhibitor in the plasma or if the patient has a very low fibrinogen level
how do abnormal platelet disorders present?
bleeding is very superficial - mucosal, skin, petechiae
how do abnormal coagulation factor disorders present?
joint bleeding
deep tissue bleeding
what is the inheritance of hemophilia?
X-linked recessive –> occur more in males
what causes hemophilia?
gene mutations that often run in families, can occur de novo so no FHx of hemophilia does not r/o
what are the 2 typs of hemophilia?
A = deficiency of factor VIII
“hemophilia eight”
B = deficiency of factoe IX
what is christmas disease?
hemophilia B
deficiency of factor IX
patient presents with spontaneous or easy bruising, recurrent joint bleeds, prolonged PTT, all other bleeding tests were normal.
hemophilia
how can you screen for hemophilia?
PTT will be prolonged
factor VIII & IX are both part of intrinsic pathway
what is the main treatment for hemophilia?
replacement factor VIII or IX
what is Desmopressin?
dDAVP
analog of ADH with no pressor activity (no increase in BP)
increases vWF and factor VIII
used in mild hemophilia A
what triggers the release of factor VIII and vWF from Weibel-Palade bodies?
desmopressin
what is a key s/e of desmopressin?
flushing, headache from vasodilation
what else can desmopressin be used for?
von Willebrand disease
Central DI (mimics ADH)
bedwetting - decreaseses urine volume
aminocaproic acid
antifibrinolytic drug
plasminogen can’t be activated to plasmin
less breakdown of formed clots - allows for whatever factor VIII or IX is available in the patients plasma to work more effectively because plasmin is not breaking down whatever fibrin clots can be formed
what is cryoprecipitate?
obsolete therapy for hemophilia A before factor VIII was readily available
precipitate that forms when FFP is thawed
separated from plasma by centrifugation
what clotting factors does cryoprecipitate contain?
factor VIII, fibrinogen (mostly)
also factor XIII and vWF
cryoprecipitate is often used as a source of what in the event of DIC, or massive trauma with blood transfusions?
fibrinogen
what are coagulation factor inhibitors?
antibodies directed against a clotting factor
either inhibit activity or increase clearance of clotting factor
inhibitors of factor VIII most common
coagulation factor inhibitors often occur in association with what?
malignancy
post-partum
autoimmune disorders
how can coagulation factor inhibitors be treated?
prednisone
how can you tell the difference between hemophilia A and coagulation factor inhibitors?
mixing study
patients serum is mixed with normal serum to see if the PT and PTT normalize
if prolonged PTT, then it is a coagulation factor inhibitor
what does vitamin K deficiency result in?
bleeding
what are the vitamin K dependent factors?
II, VII, IX, X
key lab findings of vitamin K deficiency
elevated PT/INR
can see elevated PTT
normal bleeding time
why is PT/INR the most sensitive test for vitamin K deficiency?
all the vitamin K dependent factors are part of both extrinsic and extrinsic pathways, but factor VII has the shortest half life, so the factor VII level will be the first to fall when a patient becomes vitamin K deficient, making the extrinsic pathway much more sensitive to vitamin K deficiency
vitamin K deficiency causes
dietary deficiency is rare bc GI bacteria produce sufficient quantities
warfarin (antagonizes vit. k)
antibiotics (deplete GI bacteria)
newborns (sterile GI tract)
malabsorption (vit. K is fat sol.)
how can blood transfusions cause a coagulopathy?
large volume of transfusions –> dilution of clotting factors
packed RBCs are used for blood transfusions which are devoid of plasma/platelets
administered saline or IVF with packed RBCs - no clotting factors
treated with FFP
how does liver disease result in a coagulopathy?
- loss of clotting factors:
* advanced liver disease decreases clotting factor synthesis – except for factor VIII because it is produced in endothelial cells - thrombocytopenia
- decreased hepatic synthesis of thrombopoietin
- platelet sequestration in spleen from portal HTN
what bleeding test is more sensitive to liver disease?
PT (vitamin K)
