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What is meant by "hemolysis?"
lysis of RBC
What are 3 consequences of hemolytic anemia?
Reticulocytosis, increased erythropoiesis in the marrow, accelerated RBC turnover
What are the 3 classifications of hereditary disorders that can lead to hemolytic anemia?
Membrane defects (hereditary spherocytosis and hereditary ellipsocytosis), Abnormalities in RBC enzymes (G6PD deficiency, Glycolytic pathway enzyme deficiencies, glutathione pathway deficiency), and Hb synthesis abnormalities (quantitative: thalassemias, qualitative: HbS, HbC, HbE)
What are the two classifications of acquired hemolytic disorders?
Immune (infections, alloantibodies and autoantibodies) and Non-immune (mechanical damage, physiochemical damage, membrane abnormalities)
What are the 3 clinical classifications for hemolytic disorders?
- 1. Cytoplasmic (Hb, enzymes(
- 2. Membrane (structural/shape and surface (immune mediated))
- 3. Extrinsic (mechanial, burns, toxins)
What is meant by intravascular hemolysis?
Lysis within the circulation
What is meant by extravascular hemolysis?
Removal by spleen and reticuloendothelial system (spleen, BM, liver and lungs)-> exaggeration of normal 'filtering' function
How does EPO increase the production of RBCs?
It upregulates the Bcl-2 family (via stat-5) to block apoptosis of CFU-E and proerythroblasts
What organs/tissues in the body can remove damaged or senescent RBCs?
The spleen and other tissues of the RES (liver, marrow, lungs)
What is the turnover of RBCs in the body?
What is released in RBC destruction?
Heme, globin and iron
Where is heme degraded to bilirubin?
The tissues of the reticuloendothelial system
What organ turns unconjugated bilirubin to conjugated bilirubin? What is bilirubin conjugated to? How is conjugated bilirubin excreted?
conjugated by the liver by being joined to mono + diglucuronides. It is then excreted mostly in the feces and some in the urine.
It what form is iron that is taken back up the the reticuloendothelial system stored?
Ferritin and hemosiderin
What happens to Hb released in intravascaular hemolysis?
Free Hb bound by haptoglobin complex taken up by the reticuloendothelial system. Excess free Hb may result in hemoglobinemia and hemoglobinuria.
What lab tests are used to measure RBC breakdown?
Bilirubin (total and conjugated), LDH, haptoglobin and hemoglobinemia
What test is used to measure RBC sequestration?
51Cr RBC sequestration
What test is used to measure RBC circulation?
Hb/HCT and/or 51Cr RBC survival studies
What are the signs and symptoms of hemolytic anemia?
Anemia and fatigue, fevers and chills (actue hemolytic episodes), jaundice: bilirubinemia (esp. unconjugated), hemoglobinuria (brown urine), hemoglobinemia (pink/red plasma)
What would you expect to see on a physical exam in someone with hemolytic anemia?
Splenomegaly (from sequestration), haptomegaly (less common, but seen in chronic cases), lymphadenopathy (not common unless associated with lymphoproliferative diseases like lymphoma or collagen vascular disease)
True or false: WBC and platelets are usually affected in hemolytic anemia.
False - usually not affected and no reactive changes seen.
What tests would you order to diagnose hemolytic anemia?
- 1. CBC, Hb, and RBC size
- 2. Reticulocyte count
- 3. Peripheral blood film looking for: spherocytes, shicstocytes, reticulocytosis, and nucleated RBCs
- 4. Plasma and urine Hb levels
- 5. Bilirubin tests and urine hemosiderin in chronic hemolysis)
- 6. Intracellular enzymes (lactase dehydrogenase)
- 7. Serum haptoglobin (binds free Hb, decreased)
- 8. BM exam to assess Fe stores and erythropoiesis
- 9. RBC survival tests
- 10. Immnohematologic testing for allo- and auto-antibodies
- 11. and other tests for membrane proteins, fragility, enzymopathies, infection
What conditions can lead to spherocytes?
hereditary spherocytosis, autoimmune hemolytic anemia (AIHA), ABO and fetal-maternal incompatibility, burns or thermal injury
What conditions lead to target cells?
liver disease, post splenectomy, hemoglobinopathies
What conditions lead to cell fragments?
- DIC, TTP, and HUS
- (Disseminated intravascular coagulopathy, thrombotic thrombocytopenic purpura, and hemolytic uremic syndrome)
How is hereditary spherocytosis inherited?
What genetic defects lead to hereditary spherocytosis?
Defects in RBC membrane structural proteins (spectrin, ankryin, Band 3 protein and protein 4.2)
What are some of the effects of spherocytosis on the integrity of the RBC?
It has decreased deformability, increased rigidity and increased trapping and clearance by the spleen
What are the clinical features of hereditary spherocytosis?
Anemia of variable severity, splenomegaly, jaundice, pigment stones
How do you treat hereditary spherocytosis?
Give folate and a splenectomy in severe cases after vaccinating against encapsulated bacteria and giving penicillin prophylactically
What would you expect to see on a CBC for hereditary spherocytosis?
Increased reticulocytes resulting in an increased MCV
What would you expect to see on a film (smear) for hereditary spherocytosis?
Spherocytes and polychromasia
How would you expect bilirubin and haptoglobin to change in hereditary spherocytosis?
Unconjugated bilirubin would be increased and haptoglobin would be decreased.
How do you distinguish hereditary spherocytosis from immune-mediated hemolytic anemia?
Through a Coomb's test, aka. a direct antibody test. This should be negative for hereditary spherocytosis.
True or false: you can order specific tests for band 3 protein, that will also pick up ankyrin and spectrin defects to help diagnose hereditary spherocytosis.
How does Glucose 6-phosphate dehydrogenase (G6PG) deficiency lead to hemolysis?
Normally, endogenous oxidants are inactivated by glutathione. Impaired production of glutathione in G6PG causes oxidative injury which leads to hemolysis.
How is G6PD inherited?
What environmental factors can induce hemolysis in people with G6PD?
Infections (increase ROS), and drugs (such as antimalarials, sulfonamides, or large doses of ASA)
What kinds of cell deformities would you expect to see on a film for a patient with G6PD?
Heinz bodies from oxidization of sulfhydryl groups on Hb, as well as Bite and Blister cells from filtering action by phagocytes in the spleen.
True or false: young cells are more susceptible to hemolysis in patients with G6PD because younger cells have decreased enzyme levels.
False: older cells are more susceptible because of decreased enzyme levels
How to you diagnose G6PD deficiency?
How do you treat G6PD deficiency?
Avoid precipitants. Give folate. Splenectomy in severe cases.
What populations are susceptible to more severe G6PD hemolytic anemia?
G6PD A- variant found in Black males in USA. Similar variants in people of mediterranean descent. In general, drug induced hemolysis is more common in males than females.
How does immune hemolytic anemia (IHA) lead to intravascular and extravascular hemolysis?
Through Allo or Auto Abs or complement (C') or other immune complexes binding to RBCs.
What are examples of alloimmune immune hemolytic anemia?
- Hemolytic disease of the newborn in Rh- sensitized mothers
- Immediate hemolytic transfusion reactions
- Delayed hemolytic transfusion reactions (5-10 days after transfusion)
What is the mechanism of action of autoimmune hemolytic anemia?
Antibodies made to surface antigen on own RBCs
Describe the mechanism of action of Warm AIHA (autoimmune hemolytic anemia).
Antibodies bind RBCs at 37 degrees C. The antibodies are primarily IgG and don't bind complement. Hemolysis is mostly extravascular. Opsonization of RBC via auto-Abs in the spleen and reticuloendothelial system.
Describe the mechanism of action of Cold AIHA.
Antibodies bind RBCs at 4-30 degrees C. Usually IgM is involved and it fixes complement. Hemolysis is usually extravascular (only complement detected)
What is the best diagnostic test or AIHA?
Direct Antibody Test (Direct Coomb's test) is positive. This can detect the presence of IgG and/or C3 on the patient's RBC.
What are the primary and secondary causes of warm AIHA?
Most cases are idiopathic (60%) and secondary causes include autoimmune syndromes, lymphoproliferative disease, drugs (ex. penicillin), and infection (chronic Hep C)
What do you expect to see on a blood film for warm AIHA?
spherocytes, RBC membrane removed by phagocytes, degreased surface to volume ratio
How do you treat warm AIHA?
- 1st line: steroids
- 2nd line: splenectomy
- 3rd line: other immunosuppressants
What conditions are associated with cold AIHA?
infections (mycoplasma pneumoniae or mononucleosis) or B cell lymphoid malignancies
How do you treat cold AIHA?
treat the underlying cause, steroids. A splenectomy is NOT effective.
What type of AIHA is more common?
Warm at 70%
What are possible causes of mechanical cell trauma?
- mechanical valves. High shear stress e.g. damaged valves or paravalvular leaks. Traumatic: repetitive physical trauma (marathon)
- Microangiopathic hemolytic anemia (MAHA)
What are the effects of MAHA?
- Systemic activation of coagulation system: (+INR/PTT, -Fib),
- Abnormal platelet endothelial interactions: thrombotic thrombocytopenia purpura, hemolytic uremic syndrome
- Endothelial cell injury: vasculitis, collagen vascular disease, pre-eclamsia, malignancy, malignant HTN
What are the 3 mechanisms by which mechanical trauma to RBCs can occur via shear stress?
- Shear stress because of high pressure gradients
- Shear stress because of intravascular coagulation - fibrin stands
What do you expect to see on a film for mechanical trauma?
RBC fragments or schistocytes
True or false: Mechanical trauma leads to intravascular hemolysis
How can malaria lead to hemolytic anemia?
Merozoites escape by lysing the RBC, causing hemolytic anemia. Hyperplasis of the reticularendothelial system leads to massive splenomegaly.
How can bacterial products lead to hemolytic anemia? What would you expect to see on a blood film in this case?
- Clostridial sepsis: release of enzymes that degrade phospholipids of the RBC membrane
- You would expect to see Microspherocytes (which are also seen in burns and thermal injury)
What do you expect to see on a blood film for thermal injury?
RBC damage by direct heat and microspherocyte formation
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