Heme/Onc 1 Flashcards
What is the first line defense against bleeding?
Vasoconstriction
Key mediator: Endothelin
What is Endothelin?
Potent vasoconstrictor released by endothelial cells near site of damage
Endothelin receptor blockers are used to treat what condition?
Pulmonary hypertension
Where are coagulation factors synthesized?
Liver
What do many coagulation factors activate to become?
Serine proteases
What do coagulation factors form when triggered by endothelial damage?
Fibrin to prevent blood loss
What is Tissue Factor?
Glycoprotein
Constitutively expressed in sub-endothelial cells
What is the major activator of the coagulation system?
Tissue factor (exposed by tissue damage)
How is Prothrombin Time and INR measured?
Tissue factor added to blood sample, time to clot = PT
How does thrombin make more thrombin?
Activates cascade via positive feedback: Activates Factor V, XI, and VIII
Where is Factor VIII produced?
Endothelial cells (not the liver)
Von Willebrand Factor is produced by?
Endothelial cells and megakaryocytes
Factor VIII circulates bound to what?
Von Willebrand Factor
Increases Factor VIII plasma half life
What are the 2 multicomponent complexes that convert X to Xa?
Extrinsic Xase, Intrinsic Xase
Require phospholipids (TF bearing cells or platelets) and calcium
What is Extrinsic Xase comprised of?
Phospholipid: TF-bearing cells, Enzyme: Factor VIIa, Co-factor: Tissue factor, Substrate: Factor X
What is Intrinsic Xase comprised of?
Phospholipid: Platelets, Enzyme: Factor IXa, Co-factor: Factor VIII (VIIIa), Substrate: Factor X
What is added to blood samples to prevent clotting?
EDTA (binds calcium)
Calcium is also called?
Factor IV (required for clot formation)
What is the function of Factor XIII?
Crosslinks fibrin and stabilizes fibrin plug
Requires Ca2+
What activates Factor XIII formation?
Thrombin (IIa) formation
What is Factor XII also called?
Hageman factor
What activates Factor XII?
Contact with negatively charged substances
How is the Activated Partial Thromboplastin Time (PTT) measured?
Add plasma to (-) charge substance (silica), time to form clot = PTT
What peptide hormone is required for normal function of the intrinsic pathway?
Kinins (circulate as inactive precursors due to short half life)
What activates kininogens?
Kallikreins
What are 3 effects of bradykinin?
Vasodilator, Increases vascular permeability, Pain
Bradykinin is degraded by?
ACE and C1 inhibitor protein (part of complement system)
What is a dangerous side effect of ACE inhibitors?
Angioedema
What can C1 inhibitor deficiency lead to?
Hereditary angioedema
What are 2 functions of Factor XII?
Activates clotting and produces bradykinin
Does not have a lot of physiologic significance
What happens in Prekallikrein Deficiency?
XII cannot activate normally, markedly prolonged PTT
No bleeding problems because Factor XII does not have a lot of physiologic significance
What activates the Kinin System?
Factor XII
What are 3 important deactivators of coagulation?
Antithrombin III, Proteins C and S, Tissue factor pathway inhibitor
Antithrombin III inhibits what proteins?
Serine proteases
Which factors are inhibited by Antithrombin III?
Factors II, VII, IX, X, XI, XII
What produces and activates Antithrombin III?
Liver
Activated by heparin sulfate molecules made by the endothelium
What is the basic mechanism of heparin drug therapy?
Mimics heparin sulfate and activates antithrombin III
What does deficiency of Antithrombin III lead to?
A hypercoagulable state
What produces Protein C and S?
Liver
What activates Protein C?
Thrombomodulin (cell membrane protein on endothelial cells) and Thrombin Complex
Activated Protein C primarily inactivates which factors?
Va and VIIIa
What does Tissue factor pathway inhibitor inactivate?
Xa
Mechanisms: directly binds, Binds TF/VIIa complex → prevents X activation
What plasma levels are increased with heparin administration?
Tissue factor pathway inhibitor (may contribute to antithrombotic effect)
Are Protein C and Protein S zymogens?
Yes, No
Where is Plasminogen synthesized?
Liver (as a zymogen)
What is the main role of plasmin?
Breakdown of fibrin
What are 3 plasminogen activators?
Tissue plasminogen activator (tPA), Urokinase, Streptokinase (streptococcal protein)
Tissue plasminogen activator (tPA) and urokinase are used as drug therapy for?
Acute MI and stroke
What does plasmin break down fibrin into?
Fibrin degradation products and D-dimers
What does the presence of D-dimers indicate?
Clot breakdown (indicates breakdown of crosslinked fibrin from XIII)
Fibrin degradation products (FDPs) can be elevated in the absence of a clot from?
Fibrinogen breakdown
What is the underlying mechanism of Primary Fibrinolysis?
Overactive plasmin causes ↑ FDP with normal D-dimer
Hyperfibrinolysis: Plasmin breakdown of fibrinogen but not fibrin (no clot present)
What is a complication of Primary Fibrinolysis?
Can deplete clotting factors → increase PT/PTT with bleeding
What are 2 conditions that can lead to Primary Fibrinolysis?
Prostate cancer: release of urokinase, Cirrhosis: Loss of alpha2 antiplasmin from liver
Which clotting factors are Vitamin K dependent?
II, VII, IX, X, C/S
What does Vitamin K deficiency lead to?
Bleeding
What is the mechanism of Warfarin?
Vitamin K antagonist
What is Erythrocyte Sedimentation Rate increased in?
Inflammatory conditions (factors stick together and settle faster)
What are acute phase reactants?
Serum proteins from the liver that rise in inflammation or tissue injury
Driven by cytokines
What are 3 examples of acute phase reactants?
Ferritin, Plasminogen, C reactive protein (binds bacteria; activates complement)
What forms a thrombus?
Fibrin and Activated platelets
What drives platelet production?
Thrombopoietin (TPO), produced mostly in liver
What can activate platelets?
Endothelial injury (exposure to subendothelial collagen) and stimuli from other activated platelets
What are the 3 steps to form a platelet plug?
Adhesion to sub-endothelium, Aggregation: Platelet-platelet binding, Secretion: Release of granule content
Von Willebrand Factor is synthesized by?
Endothelial cells and megakaryocytes
Where is Von Willebrand Factor stored?
Weibel–Palade bodies in endothelial cells, Alpha granules in platelets, Some found in plasma
When is Von Willebrand Factor released?
During vascular injury
What are 3 functions of Von Willebrand Factor?
Carrier protein for VIII, Binds platelets to damaged epithelium, Binds activated platelets together (aggregation)
What is the mechanism of platelet adhesion?
Vascular damage exposes subendothelial collagen → collagen binds vWF → vWF binds GP1b
Platelet Aggregation is mediated by what receptor?
GPIIb/IIIa receptor
What is the mechanism of Platelet aggregation?
Platelet activation → GPIIb/IIIa changes conformation and becomes capable of binding → binds fibrinogen or vWF → links platelets together
What activates platelet granules?
Platelet binding to collagen and granule contents from other platelets
What granules are most abundant in Platelets?
Alpha granules- Fibrinogen, vWF, and platelet factor 4
What do Dense granules in platelets contain?
ADP, Calcium, Serotonin
What is the mechanism of Heparin induced thrombocytopenia?
Antibodies formed against PF4/heparin complex → platelet activation → diffuse thrombosis + low platelets from consumption
What is the serotonin release assay?
Screening test for Heparin induced thrombocytopenia (HIT)
Donor platelets radiolabeled with 14C-serotonin → add patient serum and heparin → excessive serotonin release if HIT antibodies present
Adenosine Diphosphate (ADP) binds to what 2 receptors?
P2Y1 and P2Y12 (GPCR)
What happens when ADP binds P2Y1 or P2Y12 receptor?
↓ cAMP formation
P2Y1: Calcium release, change in platelet shape; P2Y12: Platelet degranulation, ↑ aggregation
Clopidogrel, prasugrel, ticlopidine, and ticagrelor are what type of drugs?
P2Y12 receptor blockers
What is thromboxane A2?
A powerful platelet activator
What is the mechanism of Aspirin in platelet activation inhibition?
Inhibits COX → ↓ TXA2 → inhibits platelet activation
How is thromboxane formed?
Lipids in cell membrane → arachidonic acid (AA) via phospholipase A2 in endothelial cells near damaged endothelium → AA released and converted to TXA2 by platelets (COX)
What does the bleeding time test?
Test of platelet function
Small cut on patient’s arm, filter paper applied until bleeding stops (rarely done in modern era)
Arterial thrombosis can present as?
Stroke, Myocardial infarction, Ischemic limb
What is Virchow’s triad?
3 factors that lead to formation of a thrombus: Endothelial damage, Stasis of blood, Hypercoagulability
What are Common Hypercoagulable States?
Post Op, Fall/Hip Fracture/Trauma, Long plane flight, Malignancy, Decreased activity, surgery, bed rest, Pregnancy, OCP, Elevated homocysteine, Nephrotic syndrome, Smoking
Why does OCP cause a Hypercoagulable State?
Estrogen increases production of coagulation factors
During pregnancy, which clotting factors are increased/decreased?
Increased fibrinogen, Decreased protein S
What can increase the levels of homocysteine?
Folate/B12/B6 deficiency, Homocystinuria (cystathionine beta synthase deficiency)
What can lower the levels of homocysteine?
Folate
Why is Nephrotic syndrome a Hypercoagulable state?
Loss of anti-clotting factors in urine (ATIII)
What are 4 Inherited Hypercoagulable Conditions?
Factor V Leiden, Prothrombin 20210 gene mutation, Protein C deficiency, Antithrombin III deficiency
What inhibits Factor V normally?
Activated protein C (APC)
What is the mechanism of Factor V Leiden Mutation?
Abnormal factor V, not inactivated by APC → hypercoagulability
Point mutation in factor V gene → single amino acid change
What is Prothrombin 20210 gene mutation?
Guanine to adenine change in prothrombin gene
Leads to increased prothrombin levels → hypercoagulable state
What are 3 causes of acquired Antithrombin III Deficiency?
Impaired production (liver disease), Protein losses (nephrotic syndrome), Consumption (DIC)
How does Antithrombin III Deficiency classically present?
Heparin resistance
What condition is Protein C Deficiency associated with?
Warfarin skin necrosis
Thrombosis of the skin tissue (large dark purple skin lesions)
What is the mechanism of Antiphospholipid Syndrome?
Caused by antiphospholipid antibodies
Occur in association with lupus
What are 3 clinical consequences of Antiphospholipid Syndrome?
Increased risk of venous and arterial thrombosis, Increased PTT, False positive syphilis (RPR/VDRL)
What are the 3 antibodies in Antiphospholipid Syndrome?
Anti-cardiolipin, Lupus anticoagulant, Anti-β2 glycoprotein
Which antibody in Antiphospholipid Syndrome causes a false positive syphilis test?
Anti-cardiolipin
Lupus anticoagulant interferes with which coagulation assay?
Falsely elevated PTT
Lupus Anticoagulant binds Phospholipid, which is required in coagulation cascade
How are antibodies detected in Antiphospholipid Syndrome?
Anti-cardiolipin, Anti-β2 glycoprotein: ELISA testing, Lupus anticoagulant: Detected indirectly through coagulation assays
What is needed to perform PTT assay?
Patient serum, Contact factor i.e. silica, Phospholipid, Ca2+
What is a Mixing study?
Add patient’s serum with normal serum, measure if PTT remains abnormal or is normalized
What is the result of a mixing study in Antiphospholipid Syndrome?
Falsely elevated PTT
What is Anti-β2 glycoprotein testing?
ELISA testing
How is Lupus anticoagulant detected?
Detected indirectly through coagulation assays
What is needed to perform a PTT assay?
Patient serum, Contact factor (i.e. silica), Phospholipid, Ca2+
What is the result of a mixing study in Antiphospholipid Syndrome?
PTT will not correct
What is the result of a mixing study in a clotting factor deficiency?
PTT corrects to normal
What are 2 other tests to detect Lupus Anticoagulant if PTT is normal?
Dilute Russell viper venom time, Kaolin clotting time
What is the diagnostic criteria for Antiphospholipid Syndrome?
One laboratory plus one clinical criteria: Lab criteria: 2 positive results of antibody detection, Clinical: thrombosis, fetal death after 10 weeks, >3 consecutive fetal loss before 10 weeks
What is Hypercoagulable Workup?
Panel of tests for hypercoagulable states
Controversial because expensive and rarely changes management
What tests are included in Hypercoagulable Workup?
Antithrombin level, Protein C and S levels, Factor V Leiden gene mutation, Prothrombin gene mutation, Antiphospholipid antibodies, Cancer screening
What is Normal PT/PTT? What is INR?
PT: ~10s, PTT: ~30s
INR = Patient PT/Control PT
What is the common type of bleeding with abnormal platelets?
Tends to be more superficial: Mucosal bleeding, skin bleeding, petechiae
What is the common type of bleeding with abnormal coagulation factors?
Joint bleeding, deep tissue bleeding
What is the inheritance pattern of hemophilias?
X-linked recessive (mutations can run in family or occur de novo)
What factor deficiency is seen in Hemophilia A/B?
Hemophilia A: Deficiency of factor VIII, Hemophilia B: Deficiency of factor IX
What are 2 common symptoms of Hemophilia?
Recurrent joint bleeds, Spontaneous or easy bruising
What coagulation assay(s) are abnormal in Hemophilia?
Prolonged PTT, PT, bleeding time, platelet count all normal
What is the treatment for Hemophilias?
Replacement factor VIII and IX, Desmopressin, Aminocaproic acid, Cryoprecipitate
What is Cryoprecipitate used as a source of?
Fibrinogen
Used in DIC, massive trauma with blood transfusions
What are 2 side effects of desmopressin?
Flushing, Headache
has vasodilating properties
Desmopressin can also be used to treat what 3 conditions besides Hemophilia?
Central diabetes insipidus, von Willebrand disease, Bed wetting (decreases urine volume)
What are Coagulation Factor Inhibitors?
Antibodies that inhibit activity or increase clearance of clotting factors
Which Coagulation Factor Inhibitor is most common?
Inhibitors of factor VIII most common
Coagulation Factor Inhibitors often occur in association with what 3 conditions?
Malignancy, Post-partum, Autoimmune disorders
What is the clinical presentation of Coagulation Factor Inhibitors?
Similar to hemophilia, bleeding + prolonged PTT
What is the result of a mixing study in a patient with Coagulation Factor Inhibitors?
PTT will still be elevated because the VIII is being inhibited/cleared
What are 3 key lab findings in Vitamin K Deficiency?
Elevated PT/INR, Elevated PTT (less sensitive), Normal bleeding time
What are 4 common causes of Vitamin K Deficiency?
Antibiotics, Newborn, Malabsorption, Warfarin
Why can Blood Transfusion sometimes cause coagulopathy?
Large volume transfusions dilute the clotting factors
Packed RBCs have no plasma/platelet, Saline or IV fluids also have no clotting factors
What is the treatment for Blood Transfusion Coagulopathy?
Fresh frozen plasma
Which clotting factor is not produced in the liver?
Factor VIII
What coagulation assay findings would you see in liver disease?
Increased PT (more sensitive, VII is first to decrease), Increased PTT
Where is Thrombopoietin produced?
Liver
What is the mechanism of Glanzman’s Thrombasthenia?
Deficiency IIb/IIIa → no platelet aggregation
What is the mechanism of Bernard-Soulier?
Deficiency Ib → Platelets cannot bind vWF (no adhesion)
What is the mechanism of Wiscott Aldrich?
Impaired T cell cytoskeleton function → Immunodeficiency
What is the inheritance pattern of Glanzman’s Thrombasthenia?
Autosomal recessive
What is the inheritance pattern of Bernard-Soulier?
Autosomal recessive
What is the inheritance pattern of Wiscott Aldrich?
X linked
What are key diagnostic findings in Glanzman’s Thrombasthenia?
Prolonged bleeding time, Blood smear: Isolated platelets (no clumping), Absent platelet aggregation in response to stimuli
What are 3 key diagnostic findings in Bernard-Soulier Syndrome?
Results in large platelets on blood smear, Prolonged bleeding time, Thrombocytopenia
What is the classic triad seen in Wiskott-Aldrich Syndrome?
Immune dysfunction, Eczema, decreased platelets
What is Idiopathic thrombocytopenic purpura (ITP)?
Disorder of decreased platelet survival
Commonly caused by anti-GPIIB/IIIA antibodies → platelet consumption by splenic macrophages
How to diagnose Idiopathic thrombocytopenic purpura (ITP)?
Diagnosis of exclusion
What are 3 treatments for Idiopathic thrombocytopenic purpura (ITP)?
Steroids, IVIG, Splenectomy
What is Thrombotic thrombocytopenic purpura?
Disorder of small vessel thrombus formation which consumes platelets → thrombocytopenia
What protein is defective in Thrombotic thrombocytopenic purpura?
ADAMTS13: vWF cleaving protease, prevents thrombotic occlusion
Where are large multimers of vWF stored?
Endothelial Weibel-Palade bodies, Platelet α-granules
released into serum as multimers
What is the usual cause of Thrombotic thrombocytopenic purpura?
Acquired autoantibody to ADAMTS13
What causes Microangiopathic hemolytic anemia (MAHA)?
Shearing of RBCs as they pass through thrombi in small vessels
What is seen on blood smear in Microangiopathic hemolytic anemia (MAHA)?
Schistocytes
Microangiopathic hemolytic anemia (MAHA) is seen in what 3 conditions?
TTP, DIC, HUS
What are the 4 clinical features of Thrombotic thrombocytopenic purpura?
Fever, Neurological symptoms: HA, confusion, seizures, Renal failure, Petechiae
What are 5 lab findings in Thrombotic thrombocytopenic purpura?
Hemolytic anemia, Thrombocytopenia, Schistocytes on blood smear, Normal PT/PTT, May see elevated d-dimer
What is the clinical presentation of Hemolytic Uremic Syndrome?
MAHA, thrombocytopenia, acute kidney injury
Usually no fever or CNS symptoms
Hemolytic Uremic Syndrome is a complication of what infection?
E. Coli O157:H7 infection (Shiga-like toxin causes microthrombi)
Hemolytic Uremic Syndrome is commonly seen in what age group?
Children
What is the underlying mechanism in Disseminated Intravascular Coagulation?
Widespread activation of clotting cascade, Diffuse thrombi (platelets/fibrin) → ischemia, Destruction of red blood cells → anemia (MAHA), Consumption of clotting factors and platelets
What 4 conditions can lead to Disseminated Intravascular Coagulation?
Obstetrical emergencies, Sepsis, Leukemia (especially acute promyelocytic leukemia), Rattlesnake bites
What are lab findings in Disseminated Intravascular Coagulation?
Prolonged PT/PTT, bleeding time, thrombin time, Elevated D-dimer, Anemia (MAHA, schistocytes), Thrombocytopenia, low fibrinogen
What is the treatment for Disseminated Intravascular Coagulation?
Treat underlying disorder, Fresh frozen plasma, RBCs, platelets, Cryoprecipitate (for low fibrinogen)
What are 3 underlying mechanisms of Thrombocytopenia?
Decreased production, Platelet sequestration, Platelet destruction
What is normal platelet count?
150,000-400,000 /ml
When does bleeding occur in relation to platelet count?
Bleeding occurs when platelet count is <10,000