Thrombosis & Hemostasis Flashcards
PT and PTT are used to detect disorders of secondary hemostasis. What is the difference between the 2 measures?
PT measures extrinsic pathway — normal: 10-13 seconds
PTT measures intrinsic pathway — normal: 25-40 seconds
Causes of prolonged PT
Warfarin or dicoumarol use
Deficiencies of factor II, V, VII, X
Vitamin K deficiency
Fibrinogen deficiency
Liver disease
Causes of PTT prolongation
Heparin
Lupus anticoagulant (predisposes to thrombosis)
Vonwillebrand disease
Deficiencies in factors VIII, IX, XI, or XII
Causes of prolongation of both PT and PTT
Supratherapeutic dose of heparin or warfarin
DIC (PT prolonged first)
Liver disease
Factor V or X deficiency
Prothrombin or fibrinogen deficiency
Direct thrombin inhibitor
Thrombin time tests the rate of conversion of ____
Fibrinogen—>fibrin
Causes of prolonged thrombin time
Heparin
Direct thrombin inhibitor
Factor Xa inhibitor
Fibrin degradation product
Hypo- or dysfibrogenemia
Platelet aggregation studies are important in determining platelet abnormalities when platelet count is normal. The most common abnormality is seen in pts who have taken ___ or ____ due to impaired arachidonate metabolism
ASA; NSAIDs
Platelet aggregation studies assist in dx of vonwillebrand disease, storage pool disease, bernard-soulier disease, and other congenital plt d/o. In addition, what defects in platelet function are associated with uremia, dysproteinemia, and autoimmune d/o?
Uremia — impaired platelet adhesion
Dysproteinemias — interference w/platelet membrane function
Autoimmune d/o — multiple abnormalities
_____ levels are used to identify excessive fibrinolysis
_____ may be more specific than PTT-related testing and is used when antiphospholipid syndrome is suspected
Fibrinogen
DRVVT (dilute russell viper venoma time)
Presentation of hemophilia
Typically presents in childhood w/ muscle hematomas, hemarthrosis, and persistent delayed bleeding after trauma or surgery
What are target joints?
Joints which have recurrent bleeds; typically associated with hemophilias
Inheritence and deficiency associated with Hemophilia A and B
Both are X-linked
Hemophilia A = factor VIII deficiency
Hemophilia B = factor IX deficiency
Assessing factor VIII and IX levels is indicated in any male who presents with a prolonged ____ that corrects with a mixing study
aPTT
Treatment for hemophilia A or B
Factor VIII and IX deficiencies are treated w/factor replacement (recombinant or purified)
FFP is a diluted source of clotting factors with limited efficacy for high-level replacement
Describe testing for pts suspected of having vonwillebrand disease
Includes platelet function analysis (PFA), vWF antigen level, vWF activity assay, factor VIII level, and multimer study
[note: PFA and factor VIII level may be normal in mild cases]
Lab results in vonwillebrand disease concerning PT/INR, aPTT, TT, fibrinogen, D-dimer, platelet count, PFA, platelet aggregation tests, blood smear
Normal PT/INR
Normal or increased aPTT (dependent on factor VIII activity)
Normal TT, fibrinogen, D-dimer, and platelet count
PFA increased
Platelet aggregation tests are abnormal (esp to ristocetin)
Normal blood smear
Most common inherited bleeding disorder
VonWillebrand disease
Inheritance and presentation of vonwillebrand disease
Autosomal dominant
Presents w/mild to moderate bleeding evidenced by epistaxis, menorrhagia, gingival bleeding, easy bruising, and bleeding associated with surgery or trauma
General management strategies for pts with von willebrand disease
Desmopressin (DDAVP) — releases stored vWF and factor VIII from endothelial cells
Intermediate purity factor VIII concentrates — contain vWF
Cryoprecipitate — rich in vWF but risk of transfusion-transmitted infection
Testing for pts suspected of having bleeding from advanced liver disease includes PT/INR, aPTT, mixing study, TT, fibrinogen, D-dimer, platelet count, and PFA. What are the results of these tests in the case of advanced liver disease?
Prolonged PT/INR and aPTT — corrects with mixing study
TT and D-dimer increased
Fibrinogen decreased
Platelet count decreased; PFA normal or increased
[note: PT is sensitive indicator of hepatic synthetic function d/t short half life of factor VII (6 hrs), which a failing liver cannot maintain]
General management for pts with bleeding from advanced liver disease
FFP transiently replaces all coag factors but is short-lived
Cryoprecipitate is useful if fibrinogen level is <100 mg/dL
DIC is a disorder of primary and secondary hemostasis, involving widespread activation of coagulation that leads to formation of fibrin clots. Secondary fibrinolysis dissolves these fibrin clots leading to consumption of platelets and coag factors —> thrombocytopenia, clotting factor deficiencies, bleeding, and vascular injury. What are conditions associated with the development of DIC?
Infection — most commonly gram-negative sepsis but can occur with gram-positive or viral infections (i.e., HIV)
Cancer — usually mucin-producing adenocarcinomas
Obstetric complications
How would the following typically be expected to change in the setting of DIC?
PT/INR and aPTT Thrombin time Fibrinogen D-dimer Platelet count PFA Blood smear
Prolonged PT/INR and aPTT — corrects with mixing study
Prolonged TT
Decreased fibrinogen
Increased D-dimer
Decreased platelet count
Increased PFA
Schistocytes on PB
General treatment strategies for DIC
Correct the underlying cause
Pts may require FFP/cryoprecipitate to replace coag factors, or transfusion of platelets or erythrocytes
Antithrombin III is occasionally useful
Generalized d/o of microcirculation characterized by thrombocytopenic purpura, microangiopathic hemolytic anemia, fluctuating neurological signs, renal dysfunction, and fever
TTP
2 major forms of TTP
Hereditary — mutation of ADAMSTS13 gene
Acquired — autoantibodies to ADAMSTS13
Clinical features of TTP and HUS
TTP: MAHA + thrombocytopenia (<50,000) + fever + neuro sxs
Add renal failure = HUS
Pathologic lesion and peripheral blood smear finding associated with TTP
Pathologic lesion = hyaline thrombi which occlude capillaries of virtually every organ in body
PB shows schistocytes (helmet cells) d/t MAHA — “Waring blender effect”
Treatment plan for TTP
Treat causative d/o
Plasmapheresis is lifesaving in ~100%
What are the vitamin-K dependent coag factors and how does deficiency present?
Deficiency of factors II, VII, IX, X, protein C and S
Presents with bleeding and prolonged PT
Autosomal dominant condition d/t defects in gene encoding endoglin (CD105) on Chr 9 leading to thinning of vessel walls w/telangiectatic formations, AV malformations, and aneurysmal dilatations throughout the body
Hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu)