Platelets And Coagulation

Front 1

Hemostatic system
Functions

Back 1

-Maintenance of blood fluidity within normal intact vessels
-Rapid and localized thrombosis at sites of vascular injury
-Thrombus dissolution

Front 2

Hemostatic system
Components

Back 2

Vessel wall
Platelets
Plasma protein systems
-Coagulation system (fibrin clot formation)
-Anticoagulant system (regulation of coagulation proteins of clot formation)
-Fibrinolytic system (fibrin clot dissolution)

Front 3

Forces that oppose clotting

Back 3

-Negative charges on both platelets and endothelial cells (repelling each other)
-Endothelial cells release:
*Prostacyclin and nitric oxide inhibit platelet aggregation
*Heparin-like substance that aids action of antithrombin III

Front 4

Antithrombin

Back 4

converts thrombin from a pro-coagulant to an anti-coagulant 
activate protein C which inhibits part of the coagulation cascade

Front 5

primary hemostasis

Back 5

vascular injury leads to exposure of collagen and vWF on endothelium. GP1b/IX/V on the platelets binds to the collagen and vWF. Then platelets go from being a round shape to a disc shape. This activation allows them to release their granules, and this changes the shape of their other receptors, GPIIb/IIIa,
which allows the platelets to aggregate via GPIIb/IIIa-fibrin-GPIIb/IIIa bonds

Front 6

Platelet Adhesion

Back 6

Platelet adhesion mediated by von Willebrand factor (vWF)
vWF binds to the platelet receptor GP Ib-IX-V and anchors platelets to collagen
Mnemonic – picture German gentleman driving a Mercedes on I-95

Front 7

von Willebrand Factor

Back 7

Plasma protein essential for platelet adhesion
Synthesized by endothelial cells and megakaryocytes (stored in platelet alpha granules)
Complexes to factor VIII, protects it from degradation. Circulates as multimers. High molecular weight multimers are most active and non-covalently complex with factor VIII
Ultra-high molecular weight multimers undergo post-synthetic cleavage by ADAMTS-13 in the circulation

Front 8

Platelet activation and secretion

Back 8

Shape change from spherical to discoid
Release of granule contents  recruits more platelets
α-granule contents: platelet factor 4, PDGF, fibrinogen, vWF
Dense granule contents: ADP, calcium, serotonin
Conformational change of the GP IIb-IIIa receptor helps platelets link to each other (aggregation via fibrinogen)

Front 9

Thrombocytopenia (too few platelets) Mechanism

Back 9

Decreased marrow production*
Increased platelet destruction*
Splenic sequestration
Hemodilution- you have increased the liquid volume of the blood (w saline) but not the cell volume
Spurious (EDTA-pseudothrombocytopenia)- Ab formed against EDTA in the blood tube

Front 10

Know thrombocytopenia algorithm

Back 10

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Front 11

platelet clumps

Back 11

Be careful, platelet clumps can deceptively lower the platelet count. Most labs should not even report a platelet count if significant clumping is present. This can be diminished by vortexing or vigorously shaking the tube and repeating the count. Platelet clumps can be mistakenly read as white blood cells by automated analyzers causing alarm, thus the utility of the peripheral blood smear.

Front 12

satellitism

Back 12

EDTA antibodies-->platelets start clinging to neutrophils. automated analyzers can read these as giant neutrophils.

Front 13

Decreased Marrow Production
-Reduced megakaryocytes

Back 13

-Marrow infiltration: tumor (leukemia, disseminated cancer), fibrosis (CMPD), infection (granulomatous)
-Marrow aplasia: idiopathic, immune, cytotoxic drugs, chemicals (benzene), radiation
-Congenital abnormalities: (Congenital amegakaryocytic thrombocytopenia, thrombocytopenia with absent radii)

Front 14

Decreased Marrow Production-Ineffective megakaryocytopoiesis
(your making some platelets, but not like you should be.)

Back 14

-Megaloblastic anemia
-Myelodysplasia
-Drugs (alcohol, thiazides)
-Infections (measles, HIV)
-Congenital abnormalities (Wiskott-Aldrich syndrome, May-Hegglin anomaly)

Front 15

see tegrity 27:11- 29:40

Back 15

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Front 16

Congenital Thrombocytopenia

Back 16

Thrombocytopenia absent radius syndrome (TAR)
Skeletal and hematologic abnormalities is related to the simultaneous development of the heart, the radii, and the megakaryocytes at 6-8 weeks' gestation
These pts will present with a contracted wrist and need lifelong platelet transfusions.

Front 17

Wiscott-Aldrich has

Back 17

small platelets on a blood smear

Front 18

May Hegglin anomaly

Back 18

Autosomal dominant disorder with varying thrombocytopenia
Purpura-bruises all over bc they have not enough platelets
Giant platelets
Dohle body-like inclusions in neutrophils

Front 19

Wiskott-Aldrich

Back 19

Usually immunoglobulin M (IgM) deficiency
Thrombocytopenia
Small platelets
Atopy
Cellular and humoral immunodeficiency
Increased risk of autoimmune disease and hematologic malignancy

Front 20

Immune thrombocytopenia
(Increased Platelet Destruction)

Back 20

Autoantibody-mediated: autoimmune diseases (SLE), lymphomas, drugs (heparin, quinidine, sulfa compounds), infections (EBV, HIV, CMV), idiopathic (ITP)*.
Alloantibody-mediated.: fetal-maternal incompatibility, post-transfusion purpura, platelet refractoriness

Front 21

Non-immune thrombocytopenia
(Increased Platelet Destruction)

Back 21

Thrombotic microangiopathies. (DIC,TTP, HUS)
Mechanical (prosthetic materials)

Front 22

Idiopathic Thrombocytopenic Purpura (ITP)

Back 22

Autoantibodies (IgG) against membrane glycoproteins (GP IIb-IIIa and GP Ib-IX)
Antibody-coated platelets removed by mononuclear phagocyte system
Spleen is major site of removal

Front 23

What would you see on a blood smear w/ ITP?

Back 23

Large, immature platelets in peripheral smear- b/c platelet count is down and bone marrow responds by kicking out platelets that arent ready yet
Increased and immature megakaryocytes in bone marrow
Chronic ITP (more common)
Young adult women
Diagnosis of exclusion
Clinical utility of tests for platelet-associated immunoglobulins is uncertain(treat empirically)
Acute ITP
Children
Preceded by a viral illness
Self-limited and usually resolves within 6 months

Front 24

ADAMTS-13

Back 24

binding sites on endo where ADAM. binds, recognizes HMW vWF. It should cleave them. But if you have TPP, ADAMTS-13 is either not enough or not really working, it could be being inhibited by another substance. This leads to inc. platelet aggregation and adhesion- abn thrombus formation

Front 25

Thrombotic Thrombocytopenic Purpura (TTP)

Back 25

Disorder of vWF
Vascular endothelium secretes vWF in large pentamer form
Normally processed by metalloprotease (ADAMTS-13) to smaller vWF multimers
Deficiency of ADAMTS-13  TTP
Inherited – deficiency of protease
Acquired – autoantibodies to protease
Large multimers of vWF – activate platelets  inappropriate thrombus formation

Front 26

Thrombotic Thrombocytopenic Purpura (TTP)-clinical presentation

Back 26

Formation of platelet thrombi in microvasculature
Clinical pentad:
Thrombocytopenia
Microangiopathic hemolytic anemia
Neurologic abnormalities-headache, confusion
Renal abnormalities-decreased urination, elevated creatinine
You will not see any platelets in a smear. you will see schistocytes
Fever

Front 27

schistocytes

Back 27

is a fragmented part of a red blood cell. Form when RBC's are severed by fibrin. part becomes a helmet cell and the other part becomes a microspherocyte or a mishapen fragmented cell

Front 28

Diagnosis of TTP

Back 28

Draw blood for ADAMTS-13 level and test for ADAMTS-13 inhibitor BEFORE giving patient plasma transfusion
Do not delay treatment waiting for these results…

Front 29

Treatment of TTP

Back 29

Plasmapheresis to remove ADAMTS-13 inhibitor in patient plasma
Replace plasma with Fresh Frozen Plasma

Front 30

Hemolytic Uremic Syndrome (HUS)

Back 30

Infectious gastroenteritis with E. coli strain O157:H7
Shiga-like toxin damages endothelial cells-triggers thrombi formation
Widespread microthrombi, comprised primarily of platelet aggregates, throughout microcirculation
Microangiopathic hemolytic anemia due to fibrin shearing the RBCS, thrombocytopenia, acute renal failure< renal vasculature is first to get hit.

Front 31

Neonatal Alloimmune Thrombocytopenia (NAIT)

Back 31

98% of US population have platelets with the PLA1 antigen
80% of NAIT cases result from sensitization of PLA1 negative mother by fetal PLA1 positive platelets
~50% of cases affect 1st pregnancy
Increased risk of harm to fetus with each additional pregnancy  fetal thrombocytopenia can lead to intraventricular hemorrhage in brain
Treatment: transfuse fetus with PLA1 negative platelets, preferably from the mother

Front 32

Post-Transfusion Purpura (PTP)

Back 32

Antibody response in PLA1 negative individuals to PLA1 positive platelets
Classically presents as severe thrombocytopenia in a female recipient of cellular blood products, ~7-10d post-transfusion
Often prior sensitization, prior pregnancy or transfusion
Recipient’s platelets are destroyed as well (we don’t understand why) as transfused platelets causing severe thrombocytopenia
Usually platelet counts recover in several weeks

Front 33

Platelet Refractoriness

Back 33

Occurs in repeatedly transfused patients
Anti-HLA antibodies directed against class I HLA antigens, HLA-A,B (these are on platelets)
Classically presents as progressively smaller platelet count increments following transfusion (usually chemotherapy patients who require a lot of transfusion support)

Front 34

know platelet consumption graph

Back 34

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Front 35

Heparin Induced Thrombocytopenia (HIT)

Back 35

Can happen when you’re anticoagulating a patient with heparin during surgery. Immune antibody reaction against heparin-platelet factor 4 (from platelets) complex. The Ab with the complex then binds to an Fc receptor on surface of platelets, which then releases more platelet factor 4. The newly released platelet factor 4 binds to the heparin-like glycoproteins on the surface of the epithelium. Ab binds to that too. Endothelial damage. 5-14d after starting therapy
Paradoxical life-threatening thrombosis

Front 36

know evaluation of qualitative disorders 57:57

Back 36

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Front 37

Platelet Function Testing

Back 37

Measures whole blood flow through a capillary device, simulating primary hemostasis.
Measures how long it takes for a clot to form.

Front 38

Platelet Aggregation Test

Back 38

-Specimen
Platelet-rich plasma prepared from citrated blood
-Principle
Detects abnormalities of platelet function upon addition of an aggregating agent to platelet-rich plasma
-Procedure
Aggregating agent added to turbid platelet-rich plasma specimen
Aggregometer records amount of light transmitted through the specimen as platelets clump and specimen clears
(see chart on tegrity 1:01:17

Front 39

Type 1 (75%)
von Willebrand Disease (vWD)

Back 39

decrease of all polymeric forms of vWF
multimeric analysis will reveal a decrease in the gel bands (polymeric forms) Missing a big chunk of them (in type 3 you will be missing all of them)

Front 40

light transmittence test with vWD

Back 40

normal response to epinephrine, collagen, and ADP. Lower than normal response to ristocetin.

Front 41

Qualitative Platelet Disorders

Back 41

Inherited
-Bernard-Soulier Syndrome
-Glanzmann Thrombasthenia
-Storage Pool Disease
Acquired (more common)
-Drugs (aspirin, GPIIb-IIIa antagonists)
-Hematologic disorders (CMPD, MDS, acute leukemia)
-Autoimmune disorders
-Uremia

Front 42

Bernard-Soulier Syndrome

Back 42

Rare, autosomal recessive
Deficiency of GPIb-IX (attaches to vWF on endo)
Defective platelet adhesion (to vessel wall)
a smear will show Large platelets and thrombocytopenia.
Severe bleeding
Decreased aggregation with Ristocetin
(looks similar to vWD)

Front 43

Glanzmann Thrombasthenia

Back 43

Rare, autosomal recessive
Deficiency of GPIIb-IIIa
Defective platelet aggregation (platelets can’t stick to each other) with all agonists except Ristocetin
Normal platelet size and number
Severe bleeding

Front 44

Storage Pool Diseases

Back 44

More common than other inherited qualitative platelet disorders
2 subgroups
-Storage pool deficiency
Decrease in dense granules, alpha granules, or both
-Platelet release defect
Defect in signal transduction (plenty of granules, but you cant let them out.)
* You will be missing the second wave on the light transmission graph. Ristocetin is normal.

Front 45

summary of platelet aggregation light transmission tests with diseases

Back 45

Most types of vWD & Bernard-Soulier – normal aggregation with all agonists EXCEPT Ristocetin
Glanzmann’s- abnormal aggregation with all agonists EXCEPT Ristocetin
Storage pool defects – abnormal secondary wave of aggregation with all agonists EXCEPT Ristocetin
* Notice that Ristocetin is the exception to the rule in every case…

Front 46

Secondary Hemostasis

Back 46

1)Exposure of subendothelial tissue factor
2)Activation of procoagulant cascade
3)Formation of hemostatic clot to reinforce the platelet plug

Front 47

know chart pg 1 part 3, slide 1.

Back 47

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Front 48

Screening for Bleeding Disorders

Back 48

Take a detailed personal and family hemostasis history
Spontaneous bleeds
Surgical bleeding
Bruising, bleeding gums
Drug history
Physical examination-look for bruising

Front 49

Checks and Balances

Back 49

Endothelial cells release thrombomodulin which activates Proteins C and S
Proteins C and S inhibit Factors VIII and V
This halts the coagulation cascade at the final common pathway

Front 50

prostacylin and NO

Back 50

released from endo cells, inhibits platelet aggregation.

Front 51

heparin like compound on endothelial cells

Back 51

activates antithrombin, which inhibits thrombin

Front 52

thrombomodulin

Back 52

modulates thrombus. modulates thrombin, which then makes protein c become activated protein c. inhibits Va and VIIIa.

Front 53

TFPI- tissue factor pathway inhibitor

Back 53

inhibits the processes in which TF is involved

Front 54

Prothrombin Time (PT)

Back 54

Principle
To screen for abnormalities in the extrinsic (factor VII) and common (factors V and X, prothrombin, and fibrinogen) pathways
To monitor oral anticoagulant therapy
Specimen
Citrated plasma
Procedure
Plasma mixed with thromboplastin (tissue factor and phospholipid) and calcium
Photo-optical instrument detects optical density change induced by clotting
Test performed in duplicate and clotting time averaged

Front 55

Warfarin Therapy

Back 55

Vitamin K antagonist
Vitamin K is necessary to the formation of Factors II, VII, IX and X, and anticoagulant proteins C and S
Decreased vitamin K reduces the rate at which these factors and proteins are produced anticoagulation
30 to 50 % in production of clotting factors and up to 40% decrease in activity

Front 56

An isolated, elevated PT

Back 56

Factor VII deficiency or inhibitor

Front 57

An elevated aPTT

Back 57

Factor VIII, IX and XI deficiencies

Front 58

both

Back 58

Vitamin K dependent factors: II, VII, IX, X

Front 59

activated Partial Thromboplastin Time (aPTT)

Back 59

Principle
To screen for abnormalities in the intrinsic (factors VIII, IX, XI, and XII) and common (factors V and X, prothrombin, and fibrinogen) pathways
To monitor heparin therapy
Specimen
Citrated plasma
Procedure
Plasma mixed with phospholipid (partial thromboplastin), surface-activating agent (micronized silica), and calcium
Photo-optical instrument detects optical density change induced by clotting
Test performed in duplicate and clotting time averaged

Front 60

what factors does aPTT measure?

Back 60

everything but factor VII. see my drawing for a good depiction.

Front 61

what factors do both aPTT and PT measure?

Back 61

X, V, prothrombin and fibrinogen

Front 62

Hemophilia A(Factor VIII Deficiency)

Back 62

Most common severe congenital bleeding disorder (1:10,000)
Results from reduction in the quantity or activity of Factor VIII
X-linked recessive inheritance
Variable clinical severity (spontaneous hemorrhage in severe disease)
Prolonged aPTT
Diagnosis confirmed by factor VIII assay

Front 63

Hemophilia B(Factor IX Deficiency, Christmas Disease)

Back 63

Incidence 1:30,000
Results from reduction in the quantity or activity of Factor IX
X-linked recessive inheritance
Variable clinical severity (spontaneous hemorrhage with severe disease)
Prolonged aPTT
Diagnosis confirmed by factor IX assay

Front 64

Hemophilia C(Factor XI Deficiency)

Back 64

Common in Ashkenazi Jews (8% heterozygote frequency)
Results from reduction in the quantity or activity of Factor XI
Autosomal recessive inheritance- can occur in women
Mild-moderate clinical severity (spontaneous hemorrhage rare)
Prolonged aPTT
Diagnosis confirmed by Factor XI assay

Front 65

Disseminated Intravascular Coagulation (DIC)

Back 65

Uncontrolled generation of thrombin in blood  thrombi in microcirculation high mortality
Depletion of coagulation factors
(see tegrity, second half, 30:00)

Front 66

DIC causes

Back 66

Always secondary to underlying disorder
Caused by:
Excessive tissue factor activity (ie metastatic dz, burns)
Trauma (ie neurotrauma)
Infections
Obstetric disorders (ie amniotic fluid embolus)
Endothelial damage
Acute promyelocytic leukemia (APML)
Snakebites

Front 67

DIC in APML

Back 67

May be presenting sign
Promyelocytes are a normal form of maturation of neutrophils.
Toxic granules from promyelocytes  activate coagulation cascade
Patients need all-trans-retinoic acid (ATRA) to mature cells before chemotherapy lyses them

Front 68

Amniotic fluid embolus

Back 68

Poorly understood
Possibly due to anaphylactic reaction to fetal antigens
Diagnosed by presence of fetal squamous cells in the maternal pulmonary circulation

Front 69

DIC measurement

Back 69

Elevated D-dimer-
Measure of fibrin split products
Indicates clot formation and breakdown somewhere in the body

Front 70

Liver disease

Back 70

Most coagulation factors are produced in the liver
II, VII, IX, X (vitamin K dependent factors). Also V.
Liver disease causes impaired production/secretion of factors as general function of decreased protein production.
Both PT and PTT are prolonged
Factor VII is the most sensitive early marker of liver disease (and therefore – the PT is best test)

Front 71

Vitamin K Deficiency

Back 71

Many coagulation factors depend on vitamin K
Cofactor in γ-carboxylation of glutamic acid residues to Gla residues
Activities of factors II, VII, IX, and X are low
Factor V is made in the liver but does not require vitamin K
Activity likely to be normal in liver disease

Front 72

Inherited Causes of Hypercoagulability

Back 72

Activated protein C resistance (factor V Leiden)Antithrombin deficiency
Protein C deficiency
Protein S deficiency
Dysfibrinogenemias

Front 73

acquired causes of hypercoagulability

Back 73

Lupus inhibitor
Malignancy
Nephrotic syndrome
Therapy -Factor concentrates,  Heparin, Oral contraceptives
Hyperlipidemia
Thrombotic thrombocytopenic purpura

Front 74

Factor V Leiden

Back 74

Mutation that leads to inability of Factor V to be inactivated by activated protein C (APC)
Proteins C & S normally released by endothelial cells to inactivate factors V and VIII
Less control over clotting thrombi
Patients <50 y/o with 1st venous thromboembolism, unusual site, related to pregnancy or OCP’s
Test with APC (activated protein c) resistance assay or DNA test

Front 75

Antithrombin deficiency

Back 75

Autosomal dominant
Incomplete penetrance
0.2% to 0.4% of the general population
Quantitative or a qualitative effect on antithrombin
Risk of a thrombotic event (usually venous) ranges between 20% and 80%

Front 76

Protein C & S deficiencies

Back 76

Homozygous protein C deficiency
-Life-threatening neonatal thrombosis with purpura fulminans
Up to 0.5% of the general population has heterozygous protein C deficiency
-Many are symptom free
-Clinical presentations similar to that for ATIII deficiency

Front 77

Other hypercoagulable conditions

Back 77

Genetic variations of prothrombin
Associated with thrombosis
Excessively high prothrombin levels

Front 78

know chart slide 2 last page

Back 78

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