Unit 2 - Hematology, Dermatology Flashcards
What is primary hemostasis?
Formation of weak platelet plug
Mediated by interaction between platelet and vessel wall
What is secondary hemostasis?
Stabilization of platelet plug
Mediated by coagulation cascade
Steps in Primary Hemostasis
Transient vasoconstriction of damaged vessel
Platelet adhesion to surface of disrupted vessel - vWF and GPIb
Platelet degranulation - ADP and TXA2 released
Platelet aggregation - fibrinogen and GPIIb/IIIa
What are the clinical signs of disorders of primary hemostasis?
Mucosal Bleeding - epistaxis, hemoptysis, GI bleeding, hematuria, menorrhagia
Skin Bleeding - petechiae, purpura, ecchymoses, easy bruising
Disorder of primary hemostasis that involves autoimmune production of IgG against platelet antigens
Immune Thrombocytopenic Purpura (ITP)
Most common cause of thrombocytopenia in children and adults
Immune Thrombocytopenic Purpura (ITP)
Laboratory findings in Immune Thrombocytopenic Purpura
Low Platelet count
Normal PT/PTT
Increased megakaryocytes on bone marrow biopsy
Why would you remove the spleen in ITP?
Removes source of antibodies and site of platelet destruction
Treatment of ITP
Corticosteroids, sometimes IVIG (short lived effects), splenectomy in refractory cases
Disease that involves pathologic formation of platelet microthrombi in small vessels
Microangiopathic Hemolytic Anemia
In which 2 diseases do you see microangiopathic hemolytic anemia?
Thrombotic Thrombocytopenic Purpura (TTP)
Hemolytic Uremic Syndrome (HUS)
Thrombotic Thrombocytopenic Purpura is due to decreased ______
ADAMTS13 - normally cleaves vWF, in disease uncleaved vWF leads to abnormal platelet adhesion
What causes Hemolytic Uremic Syndrome?
Endothelial damage due to drugs or infection
Clinical findings in HUS and TTP
Skin and mucosal bleeding Microangiopathic hemolytic anemia - schistocytes Fever Renal Insufficiency - more common in HUS CNS abnormalities = more common in TTP
Lab findings in TTP and HUS
Thrombocytopenia with increased bleeding time
Normal PT/PTT
Anemia with schistocytes
Increased megakaryocytes on marrow biopsy
Treatment of TTP and HUS
Plasmapheresis and corticosteroids
What is Bernard-Soulier syndrome?
Genetic GPIb deficiency - impaired platelet adhesion
What is Glanzmann Thrombasthenia?
Genetic GPIIb/IIIa deficiency - impaired platelet aggregation
How does aspirin impair primary hemostasis?
Irreversibly inactivates cyclooxygenase - lack of TXA2 impairs aggregation
How are the factors in the coagulation cascade activated?
Exposure to activating substance - tissue thromboplastin activates Factor VII in extrinsic, subendothelial collagen activates Factor XII in intrinsic
Phospholipid surface of platelets
Calcium
Clinical features of secondary hemostasis disorders
Deep tissue bleeding, rebleeding after surgical procedures
What do PT and PTT measure in coagulation cascade?
PT - extrinsic (factor VII) and common (Factors II, V, X, and fibrinogen) pathways
PTT - intrinsic (factors XII, XI, IX, VIII) and common pathways
What is Hemophilia A?
Genetic factor VIII deficiency - x linked recessive
Lab findings in Hemophilia A
Increased PTT, normal PT
PTT does correct if mix plasma with normal plasma
Decreased Factor VIII
Normal platelet count and bleeding time
What is Hemophilia B?
Genetic Factor IX deficiency - similar to Hemophilia A
Disease involving acquired antibody against a coagulation factor resulting in impaired factor function
Coagulation Factor Inhibitor
Lab findings of Coagulation Factor Inhibitor
Increased PTT, normal PT
PTT does not correct if mix plasma with normal plasma
Normal platelet count and bleeding time
Most common inherited coagulation disorder
Von Willebrand Disease
Lab findings in Von Willebrand Disease
Increased bleeding time
Increased PTT, normal PT
Decreased factor VIII half-life
Abnormal ristocetin test (test platelet agglutination)
Treatment for Von Willebrand Disease
Desmopressin (ADH analog) - increases vWF release from Weibel-Palade bodies of endothelial cells
What does Vitamin K deficiency lead to?
Interruption of coagulation factors - needed to carboxylate certain factors (II, VII, IX, X, proteins C and S)
Where would you see Vitamin K Deficiency?
Newborns - lack of GI colonization
Long term antibiotic therapy - disrupts bacteria in GI
Malabsorption
What is one consequence of heparin induced thrombocytopenia?
Fragments of destroyed platelets may activate remaining platelets - thrombosis
Disease involving pathological activation of coagulation cascade
Disseminated Intravascular Coagulation (DIC) - almost always secondary to another disease process
Pathogenesis of DIC
Widespread microthrombi - ischemia and infarction
Consumption of platelets and factors results in bleeding
Lab findings in DIC
Low platelet count Increased PT/PTT Decreased fibrinogen Microangiopathic hemolytic anemia Elevated fibrin split products - D-Dimer (best screening test)
What are disorders of fibrinolysis due to?
Overactivity of plasmin - excessive cleavage of serum fibrinogen
Lab findings in disorders of fibrinolysis
Increased PT/PTT - plasmin destroys coag factors
Increased bleeding time with normal platelet count
Increased fibrinogen split products without D-Dimers
What distinguishes a thrombus from a postmortem clot?
Lines of Zahn
Attachment to vessel wall
3 major risk factors for thrombus formation (AKA Virchow Triad)
Disruption in blood flow
Endothelial Cell Damage
Hypercoagulable state
How do endothelial cells prevent thrombosis?
Block exposure to subendothelial collagen and tissue factor
Produce prostacyclin and NO - vasodilation
Secrete heparin-like molecules
Secrete tissue plasminogen activator (tPA)
Secrete thrombomodulin - redirects thrombin to activate Protein C, which inactivates factors V and VIII
Causes of endothelial cell damage
Atherosclerosis, vasculitis, high levels of homocysteine
Classic presentation of hypercoagulable state
Recurrent DVTs or DVT at a young age
How does Protein C and S deficiency cause a hypercoagulable state?
Decreased negative feedback on coagulation cascade - normally inactivate factors V and VIII
In which hypercoagulable state disease do you have increased risk for warfarin skin necrosis?
Protein C and S deficiency
Most common inherited cause of hypercoagulable state
Factor V Leiden - mutated form of Factor V that lacks cleavage site for deactivation by protein C and S
What is Prothrombin 20210A and how does it cause a hypercoagulable state?
Inherited point mutation in prothrombin, results in increased gene expression of prothrombin –> increased thrombin –> risk for thrombosis
How does ATIII deficiency lead to a hypercoagulable state?
Decreases protective effect of heparin-like molecules produced by endothelium (normally they activate ATIII which inactivates thrombin and coagulation factors)
Definition of anemia
Reduction in circulating RBC mass
Clinical signs and symptoms of anemia
Hypoxia - weakness, fatigue, dyspnea, pale conjunctiva and skin, headache, lightheadedness, angina
What causes microcytic anemias?
Decreased production of hemoglobin
Most common type of anemia
Iron Deficiency Anemia
Where does iron absorption occur?
Duodenum
Transporters for iron in GI, blood, and intracellular
GI - ferroportin
Blood - transferrin
Intracellular - ferritin
What is iron deficiency usually caused by?
Dietary lack of iron
Blood loss
Stages of Iron Deficiency Anemia
- ) Storage iron depleted - decreased ferritin, increased TIBC
- ) Serum iron depleted - decreased serum iron, decreased saturation
- ) Normocytic Anemia
- ) Microcytic, hypochromic anemia
Clinical features of Iron Deficiency Anemia
Anemia
Koilonychia (spoon shaped nails)
Pica (chewing on abnormal things like dirt)
Lab findings in Iron Deficiency Anemia
Microcyctic, hypochromic RBCs with increased red cell distribution width
Decreased ferritin, increased TIBC, decreased serum iron, decreased saturation
Increased free erythrocyte protoporphyrin
What is Plummer-Vinson Syndrome?
Iron deficiency anemia with esophageal web and atrophic glossitis
Most common type of anemia in hospitalized patients
Anemia of chronic disease
How does Hepcidin play a role in anemia of chronic disease?
Produced by liver as acute phase reactant
Sequesters iron in storage sites, making less available for hemoglobin production
Lab findings in anemia of chronic disease
Increased ferritin
Decreased TIBC
Decreased serum iron, decreased saturation
Increased free erythrocyte protoporphyrin
Anemia due to defective protoporphyrin synthesis
Sideroblastic Anemia
Where does iron end up if protoporphyrin is deficient?
Remains trapped in mitochondria - forms ringed sideroblasts
Congenital and acquired causes of Sideroblastic Anemia
Congenital - defect in ALAS
Acquired - Alcoholism (poisons mitochondria), Lead Poisoning (inhibits ALAD and ferrochelatase), Vitamin B6 deficiency (required cofactor for ALAS)
Lab findings in Sideroblastic Anemia
Increased ferritin
Decreased TIBC
Increased serum iron, increased saturation (iron overloaded state)
Anemia due to decreased synthesis of globin chains of hemoglobin
Thalassemia
Alpha-Thalassemia is usually due to which genetic defects and what are the phenotypes?
Gene deletion on Chromosome 16
1 deleted - asymptomatic
2 deleted - mild anemia with increased RBC count
3 deleted - severe anemia, HbH formed that damage RBCs
4 deleted - lethal in utero (hydrops fetalis), Hb Barts formed
Beta-Thalassemia is usually due to which genetic defects?
Gene mutations on chromosome 11
Mildest form of Beta-Thalassemia and how is it diagnosed?
Beta-Thalassemia Minor
Blood smear - microcytic, hypochromic RBCs and target cells
Electrophoresis - slightly decreased HbA with increased HbA2 and HbF
Most severe form of Beta-Thalassemia
Beta-Thalassemia Major
Clinical features of Beta-Thalassemia Major
Ineffective erythropoiesis and extravascular hemolysis (removal of RBCs by spleen) causes:
Expansion of hematopoiesis into skull (crewcut appearance) and facial bones (chipmunk facies)
Extramedullary hematopoiesis with hepatosplenomegaly
Diagnostic features of Beta Thalassemia Major
Blood smear - microcytic, hypochromic RBCs with target cells and nucleated RBCs
Electrophoresis - HbA2 and HbF with little or no HbA
Major and minor causes of Macrocytic Anemia
Major - Folate or Vitamin B12 deficiency (megaloblastic)
Minor - Alcoholism, liver disease, certain drugs (non-megaloblastic)
Where is folate absorbed in GI?
Jejunum
Causes of folate deficiency
Poor diet
Increased demand - cancer, pregnancy, hemolytic anemia
Folate antagonists - methotrexate
Clinical and Lab findings of folate deficiency
Macrocytic RBCs and hypersegmented neutrophils Glossitis Decreased serum folate Increased serum homocysteine Normal methylmalonic acid
What does Vitamin B12 bind to in small bowel and where is it absorbed?
Binds to intrinsic factor, absorbed in ileum
How long does folate deficiency take to develop vs. Vitamin B12 deficiency?
Months vs. years
Most common cause of Vitamin B12 deficiency and minor causes
Major: Pernicious Anemia - autoimmune destruction of parietal cells leads to intrinsic factor deficiency
Minor: Pancreatic insufficiency, damage to terminal ileum
Clinical and lab findings in Vitamin B12 deficiency
Macrocytic RBCs with hypersegmented neutrophils
Glossitis
Subacute combined degeneration of spinal cord
Decreased serum Vitamin B12
Increased serum homocysteine
Increased methylmalonic acid
What are the 2 major causes of normocytic anemia and how do you differentiate between the two?
Increased peripheral destruction of RBCs or underproduction of RBCs
Reticulocyte count differentiates
Corrected reticulocyte count of >3% indicates ______ while corrected reticulocyte count of
Good marrow response, peripheral destruction; poor marrow response, underproduction
Clinical and lab findings of extravascular hemolysis of RBCs (peripheral destruction)
Anemia with splenomegaly, jaundice due to unconjugated bilirubin, and increased risk for bilirubin gallstones
Marrow hyperplasia with corrected reticulocyte count of >3%
Clinical and lab findings of intravascular hemolysis of RBCs (peripheral destruction)
Hemoglobinemia
Hemoglobinuria
Hemosiderinuria
Decreased serum free haptoglobin (binds to Hb in blood)
Normocytic anemias with predominately extravascular hemolysis
Hereditary Spherocytosis
Sickle Cell Anemia
Hemoglobin C
Anemia caused by inherited defect of RBC cytoskeleton-membrane tethering proteins
Hereditary Spherocytosis
Pathogenesis of Hereditary Spherocytosis
Membrane blebs formed and lost over time - loss of membrane causes round RBCs, which are less able to maneuver through sphenoid sinuses causing macrophages to consume them
Clinical and lab findings of Hereditary Spherocytosis
Spherocytes with loss of central pallor
Increased RDW and mean corpuscular hemoglobin concentration
Splenomegaly, jaundice, increased risk for bilirubin gallstones
Increased risk for aplastic crisis with parvovirus B19 infection of erythroid precursors
What are Howell-Jolly bodies?
Howell-Jolly bodies are fragments of nuclear material in RBCs, can see when spleen is removed
What genetic mutation causes Sickle Cell Anemia?
Autosomal recessive mutation of Beta chain of hemoglobin
Glutamic acid –> valine change
What increases risk of RBCs sickling in Sickle Cell anemia?
Hypoxemia, dehydration, acidosis
Complications in Sickle Cell Anemia due to RBC membrane damage
Extravascular hemolysis
Intravascular hemolysis
Massive erythroid hyperplasia resulting in expansion of hematopoiesis into skull, facial bones & extramedullary hematopoiesis
Complications of vaso-occlusion in Sickle Cell Anemia
Dactylitis - common presenting sign in infants
Autosplenectomy
Acute Chest Syndrome - most common cause of death in adult patients
Pain Crisis
Renal Papillary Necrosis
In patients with Sickle Cell trait, where does the sickling of RBCs occur?
Renal Medulla
Lab findings in Sickle Cell Disease
Blood smear - sickle cells and target cells
Positive metabisulfite screen
Hb electrophoresis for HbS