Defects in Coagulation (Part 1) Flashcards
What two molecules are important for platelet aggregation?
Fibrinogen and GPIIb/IIIa
What molecules are important for platelet adhesion?
vWF and GPIb-alpha
collagen and GP6
Dense Granules contain ADP, ATP, Seratonin, Calcium which signal platelets to do what?
aggregate
What do platelet alpha granules contain?
- Coagulation Proteins: F-V, Fibrinogen, VWF
- Growth factors: TGF-ß and PDGF
- Platelet factor 4
Steps of Platelet Adhesion?
Endothelial damage -> Collagen exposed -> VWF sticks -> Platelets adhere
Steps of Platelet Adhesion on VWF?
flowing past location -> braking (GPIb) -> activation (GPIb) -> arrest (GPIIb/IIIa)
Consequences of platelet activation?
- Granule release Signal to other platelets
- Activation of GP IIb/IIIa that Allows platelet cohesion
- Membrane procoagulant expression forming thrombin then a clot
What are the steps in Platelet cohesion via fibrinogen bridges?
- ADP and 5-HT bind receptors on passing platelets
- Platelet recruitment/activation
- Platelets cohere via fibrinogen bridges
Result: Primary platelet plug
In general, what is the coagulation cascade?
Series of transformations of proenzymes to activated enzymes resulting in the formation of thrombin (IIa) which drives fibrin clot formation
What are the steps in the coagulation cascade?
- Initiation: TF/FVIIa activates Factor IXa & Xa: F Xa converts II to make initial thrombin (IIa)
- Amplification: Initial thrombin activates Va, VIIIa, XIa and platelets
- Propagation: XIa augments process by driving further IXa formation: IXa catalyzing further thrombin formation on platelet
- Thrombin drives transformation of fibrinogen to fibrin and cross-linking
Vitamin K dependent factors are?
Pro-coagulant: 2, 12, 9 and 10
Anti-coagulant: Protein C and S
What is the fibrinolytic system?
molecules involved in the breakdown and clearance of clots for healing part of the balancing act of hemostasis
includes t-PA, Plasminogen, α2antiplasmin, D-dimer
What general setting favor thrombosis?
Inflammation: Tissue factor and Injury: expose collagen
What does antithrombin III (heparin can help) do?
inactivates thrombin and factors 10 and 11
What does tissue factor pathway inhibitor do?
inactivates factors 7 and 10
What does thrombomodulin do?
binds active thrombin then causes activation of protein C and S which cause inactivation of factors 5 and 7 and release of PIG2, NO and adenosine which inhibit platelet aggregation
What does t-PA do?
starts the fibrinolytic cascade
What is the best screening test for coagulation defect?
Trick question!
It’s history!
What history should you take for suspected coagulation defect?
Site of bleeding (mucosal, deep, generalized oozing or bruising)
Timing of bleeding (immediate vs delayed)
Surgical history
Family history
Medications
What do you usually seen on exam?
skin: petechia, hematoma
signs of liver disease
splenomegaly
What screening tests tell you about platelets?
– Platelet count (and blood film review)
– PFA-100
What screening tests tell you about coagulation cascade?
– Prothrombin time (PT)
– Partial thromboplastin time PTT
– Fibrinogen
– Inhibitor screening (1:1 mix)
What tests are good for platelet defects?
Quantitative Defects
• Peripheral blood film
• Marrow evaluation (megakaryocytes)
• Lab studies for associated disorders – Such as Vitamin B12, PF4 ELISA, etc
Qualitative defects
• Platelet Aggregation
• others
What is thrombocytopenia?
low platelets due to decreased production or increased destruction
What causes decreased platelet production?
– Nutritional: Vitamin B12 deficiency
– Marrow failure or disease • Aplastic anemia • Myelodysplasia or Leukemia • Congenital thrombocytopenia syndromes • Marrow replacement (metastatic Ca, Gaucher’s) • Toxin/Drug/Irradiation
What causes platelet destruction?
– Non-immune: Blood Film often abnormal √
• Disseminated intravascular coagulation
– Immune
• Fab mediated: Blood Film usually normal – Immune thrombocytopenic purpura (ITP), Antiphospholipid syndrome
• Non-Fab mediated – Heparin-induced thrombocytopenia), Immune complex disease (HIV), TTP
• Innate immunity – Sepsis √
What are the two types of Immune Thrombocytopenic Purpura?
Childhood and adult
What happens in childhood Immune Thrombocytopenic Purpura?
– Abrupt onset of severe thrombocytopenia
– Antecedent viral syndrome is common
– Mechanism: Auto-antibody to platelet surface glycoproteins
– Decreased platelet survival and marrow usually shows normal to increased numbers of megakaryocytes
– Most patients recover: 50% recover within 6 weeks, 80-90% recover within 6 months
What happens in adult Immune Thrombocytopenic Purpura?
– Onset usually insidious • Minor bleeding, menorrhagia, bruising usually no obvious antecedent viral illness
– Decreased platelet survival, but most also have decreased production, despite marrow that has megakaryocytes
– Only 5% have spontaneous recovery
What about RBC and WBC in Immune Thrombocytopenic Purpura?
Blood Film: RBC and WBC usually normal with large platelets due to high turnover rate
Neo-epitope (Heparin:PF4) causes transient autoimmune disease
What disease?
Heparin-Induced Thrombocytopenia
When does Heparin-Induced Thrombocytopenia occur?
Timing consistent with immune: 4-10 days into heparin therapy
Why are we concerned about Heparin-Induced Thrombocytopenia?
- Moderate thrombocytopenia (rarely < 20,000/ul) – Suspect if platelet count falls by half
- Associated with thrombotic events– Increases risk for thrombosis 20-40 fold
What should we use to diagnose Heparin-Induced Thrombocytopenia?
Suspicion, Lab confirmation: PF-4~Heparin ELISA or SRA
What should we do to treat Heparin-Induced Thrombocytopenia?
– Stop all heparin therapy
– Begin alternative anticoagulation • Direct Thrombin Inhibitor (DTI): Argatroban, Bivalirudin
What are the major Causes of Microangiopathic Blood Film?
Thrombotic Thrombcytopenic Purpura (TTP)
Hemolytic uremic syndrome (Shiga-toxin associated-HUS, etc.)
DIC, sepsis
What is the pentad of Thrombotic Thrombcytopenic Purpura (TTP)?
– Lab abnormalities (required for diagnosis)
• microangiopathic hemolytic anemia
• thrombocytopenia
– Organ dysfunction (not required for diagnosis)
• renal failure
• mental status changes
• Fever
TTP is a clinical diagnosis
What enzyme deficiency explains most
cases of TTP?
ADAMTS13 is an enzyme that regulates VWF/platelet interactions
Acquired autoantibody or congenital
What is the treatment for TTP?
Plasma Exchange
What does the PFA-100 test screen?
Screen for platelet and VWF function via Aperture closure time
used when there is prolonged or strong bleeding history
positive test can mean VWD
What are the functions of vWF?
- Support platelet adhesion to exposed collagen (at sites of injury).
- Serve as carrier for Factor VIII – vWF maintains factor VIII in circulation. Thus: abnormalites of vWF may lead to F-VIII deficiency (long PTT).
What lab evals are diagnostic of VWD?
assay vWF
– Quantitation of VWF by immunoassay by VWF:Ag
– Quantitation of VWF function by Ristocetin cofactor assay with VWF:RCo
Congenital absence of GPIb on platelets
Bernard Soulier syndrome
Congenital absence of GPIIb/IIIa on platelets
Glanzman’s thrombasthenia
What is the method of Prothrombin Time and what pathway does it measure?
Tissue factor, phospholipid and calcium are added to citrated plasma and clotting time is measured. Reported in seconds and INR.
measures extrinsic pathway (factor 7 and on)
What is INR?
Mathematic calculation:
– Normalizes reported prothrombin time so that result is comparable across laboratories.
– Intended for warfarin monitoring
What is the method of PTT and what pathway does it measure?
Surface activator, phospholipid and calcium are added to citrated plasma and clotting time is measured
measures intrinsic pathway (factor 11 and on)
What is a 1:1 mix study and what does it tell me?
Patient plasma is mixed with normal plasma containing 100% of all factors. Clotting time is performed on the mixed sample
– If the clotting time corrects to normal, then a factor deficiency is likely
–If the clotting time remains prolonged, then an “inhibitor” is likely
What can cause isolated long PTT?
Intrinsic pathway defect
– Factor VIII, IX, XI, XII, Contact factors
– von Willebrand disease if factor 8 is low
Inhibitors:
– Heparin: accelerates antithrombin
– Lupus anticoagulant: Inhibits phospholipid dependent reactions
– Specific factor inhibitor
If PTT is prolonged and PT is normal what test should we do?
repeat PTT and a 1:1 mix
if mix corrects then assay factors 8, 9, 11 and 12 since one is deficient
What can cause isolated long PT?
• Factor deficiency:
– Factor VII
– Combination of factors: Vitamin K deficiency/Oral anticoagulant or Liver Disease
• Inhibitors:
– Factor inhibitor
– Lupus inhibitor (rare presentation)
If PT is prolonged what tests should we do?
repeat PT and 1:1 mix
if mix corrects (deficient), test liver function, factors 2,7, 5 and 10 and vitamin K level
What can cause prolonged PT and PTT?
Factor Deficiency:
– Isolated factor: X, V, II, fibrinogen (common path)
– Multiple factor deficiency from Liver disease, Vitamin K deficiency or DIC
Inhibitors:
– Isolated factor inhibitor (X, V, II)
– Drugs: Heparin, Direct Thrombin Inhibitors
– Lupus inhibitor
What factors are not tested for by screens?
factor 8
Physiologic anticoagulants: Antithrombin, Protein C, Protein S and Factor V Leiden
How can you tell if bleeding is mucocutaneous or deep?
If you can see blood = mucocutaneous
If you cannot see blood = deep (muscle, joint, etc)
Is mucocutaneous or deep the hallmark sign of defect in primary hemostasis?
mucocutaneous
What three tests can give you the most info about a bleeding disorder quickly?
CBC with dif
Coagulation studies (PT and PTT)
Peripheral blood smear
How can you treat ITP?
wait and see with kids
if severe or adult usually need steroids or IVIG
Patient has mucocutaneous and deep bleeding as well as oozing from venipuncture site. What does he have?
DIC which is an acquired syndrome characterized by systemic intravascular coagulation which causes consumptive bleeding disorder
How do you treat DIC?
correct underlying cause!
then fresh frozen plasma and platelet transfusion
What types of bleeding is common in secondary hemostasis defects?
joint, muscle, soft tissue, intracranial – all deep
