245/246 - Congenital & Acquired Hemolytic Anemias Flashcards
How long do red blood cells usually live?
90-120 days
What is the difference between extracorpuscular and intracorpuscular hemolysis?
-
Extracorpuscular = something is attacking the RBC
- Immunologic
- Mechanical
- Infectious
- Hypersplenism
-
Intracorpuscular = Something is wrong within the RBC
- Hemoglobinopathies
- Enzyme defects
- Membrane abnormalities
What hemolytic anemia will demonstrate absent CD55 and CD59 expression on flow cytometry?
Paroxysmal nocturnal hemoglobinuria (PNH)
- acquired disorder of stem cells caused by mutations in phosphatidyl-inositol-glycan A (PIG A) in the RBC membrane
- GPI protein helps anchor proteins to the lipid bilayer
- leads to complement mediated lysis of RBCs
- may have acute hemolysis at night and wake up to red urine
- Type 3 –> no GPI anchored molecules (most severe)
- Type 2 –> reduced amount
- Type 1 –> almost normal
- Treatment: stem cell transplant is curative
Which protein is deficient in Southeast Asian Ovalocytosis?
Band 3
- Southeast Asian Ovalocytosis is an autosomal dominant disease caused by Band 3 deficiency that displays mild anemia.
- Band 3 plays a critical role in chloride, and bicarbonate exchange; binds cytoplasmic membrane components
What is the only FDA-approved, commonly used drug to treat sickle cell disease?
What is its effect?
Hydroxyurea
Results in increased fetal Hb
Fetal Hb does not sickle
What is the treatment for spur cell (acanthocyte) anemia?
Liver transplant
- Spur cell anemia is caused by liver disease
- -> has a membrane defect that results in excess cholesterol, but normal phospholipid
- -> Fragility
- results in severe anemia and splenomegaly
List 3 mechanisms by which drugs can induce hemolytic anemia
-
Haptan-induced
- Antibody binds to the drug, that is bound to the RBC
- Penicillin, cephalosporin, tetracyclinc
-
Immune-complex
- Antibody binds to the drug-RBC complex (antibody forms complex w/ drug and RBC membrane component)
- Quinine, quinidine, sulfonamides
-
Autoimmune
- Drug induces formation of antibodies against RBCs
- Drug does NOT need to be bound to RBC for antibody binding
- Stopping the drug will not stop the hemolysis immediately
These are all warm autoimmune hemolytic anemias
Which inherited hemolytic anemia is most common?
Which protein is most commonly mutated in this disorder?
Hereditary spherocytosis
- Deficiency in membrane proteins
- Ankyrin >> spectrin > band 3
- -> mechanical instability, membrane loss
- Spheroid, fragile RBCs
What is the most common cause of death in children with sickle cell disease worldwide?
Infection
- People with SCD are more susceptible to infection by encapsulated bacteria (due to functional asplenia)
- Viral infections (parvovirus) may trigger an aplastic crisis
What is the mechanism of hemolysis in hereditary spherocytosis?
Increased splenic trapping
- > Erythrostasis
- > Hemolysis
Where in the body is vaso-occlusion due to RBC sickling most likely to occur?
Post-capillary venules
- This is where RBCs have the least oxygen => most prone to sickling (sickling more likely to occur when deoxygenated)
- Also, these vessels are small
- Sickling -> log jam -> more sickling -> :(((
List two medical complications associated with sickle cell trait
(one mutated copy, one normal copy)
Increased risk of:
- Chronic kidney disease
- Venous thromboembolism (VTE)
Previously thought that sickle cell trait did not cause any problems and was protective against malaria, but looks like it may confer increased risk of these conditions
What kind of immunoglobulin (IgM or IgG) is responsible for warm and cold hemolytic anemia?
- Warm: IgG (or complement)
- Cold: IgM
List 3 important proteins found in the red blood cell membrane
-
Band 3
- Transmembrane
- Binds cytoplasmic components of the RBC membrane
-
Spectrin
- Peripheral
- Supports the lipid bilayer
-
Ankyrin
- Peripheral
- Links spectrin and Band 3
Which virus may lead to an aplastic crisis in patients with sickle cell disease?
Parvovirus
What would you suspect if a patient has warm autoimmune hemolytic anemia with low reticulocytes?
Suspect secondary process, like iron deficiency
How is G6PD deficiency inherited?
X-linked recessive mutation in G6PD gene
Heterozygous 46,XX individuals may have variable expression
- G6PD plays a big role in the pentose phosphate pathway (major metabolic pathway for RBCs)
- G6PD is present in all cells, but can’t be replaced in RBCs
- RBCs w/ have decreased NADPH, decrease of the reduced form of glutathione, and decreased protection from oxidative stress
List 4 possible genotypes that can result in sickle cell disease
- Hb S/S
- Hb S/C
- Hb S/Beta null
- Hb S/Beta (+)
Wild type is Hb A/A
Basically, any combination of 2 non-A alleles can result in sickled red blood cells
What kind of antibodies are responsible for Rh hemolytic disease of the fetus/newborn?
IgG (the Ig that can cross the placenta)
- Note: ABO antibodies are IgG or IgM, but Rh hemolytic disease is more serious (but less common)*
- Fetus does not produce much ABO antigen as Rh (D) antigen*
What mutation causes paroxysmal nocturnal hemoglobinuria?
Mutation in phosphatidyl-iositol-glycan A
- Results in GPI-anchored protein deficiencies
- Proteins that protect RBC from complement destruction cannot bind (CD55, CD59)
- Results in complement-mediated lysis or RBCs
Which protein is deficient in hereditary eliptocytosis?
Alpha or beta spectrin
May result in carrier state or severe condition (hereditary pyropoikilocytosis)
List the most common acute complications of sickle cell disease
- Acute pain episodes
- Acute chest syndrome = fever, abnormal CXR, and respiratory symptoms
-
Functional asplenia
- -> increased risk of infections w/encapsulated bacteria
- Splenic sequestration
- Stroke/ CNS injury
- Aplastic crisis
End orgen damage = later complication
What RBC morphology will you see in warm antibody hemolytic anemia?
How are the RBCs destroyed?
Spherocytes
Parts of the membrane are chomped off due to antibody binding -> spherocytes
List the two hemoglobin “switches” that occur during development
Which globins are present in each type of hemoglobin?
- Embryonic Hb (δ2ε2) -> Fetal Hb (α2γ2)
- Occurs at 10 weeks gestational age
- Fetal Hb (α2γ2) -> Adult Hb (α2β2)
- Occurs after birth, around 6 months fetal Hb will be gone
What molecules mediate the hemolysis:
- Warm antibody autoimmune hemolysis:
- Cold antibody autoimmune hemolysis:
- Warm antibody autoimmune hemolysis: antibodies coat the RBCs, these RBCs are removed in the spleen (extravascular hemolysis)
- can also have complement mediated lysis of the membrane
- Cold antibody autoimmune hemolysis: occurs through complement fixation –> hemolysis is intravascular
List the 2 metabolic pathways that RBCs use to produce energy
What is the major product of each pathway?
-
Pentose phosphate pathway: NADPH
- Protection from oxidative stress
-
Glycolysis (anaerobic): ATP
- Energy!
What conditions are associated with cold antibody hemolytic anemia? (2 acute, 2 chronic)
-
Acute:
- Mycoplasma
- EBV
- Chronic
- Lymphoproliferative disorders
- Idiopathic
In a patient with sickle cell disease, what is the most common reason for presenting to the ED?
Pain crisis
- Caused by vaso-occlusive episode
On which chromosome is each genetic loci found?
- Beta-globin:
- Alpha-globin:
- Beta-globin: Chromosome 11
- Alpha-globin: Chromosome 16
Regulatory components are upstream (toward the 5’) of each locus
After RBC sickling in sickle cell disease, what is the next step in the pathogenesis that eventually leads to pain, disability, and end organ damage?
Vaso-occlusion
Most likely to occur in post-capillary venules
(lowest O2 concentration -> RBCs most prone to sickling)
What is the treatment for paroxysmal nocturnal hemoglobinuria?
Goal is to prevent complement from destroying RBCs
-
Eculizumab
- Antibody against C5
- Stem cell transplant is curative
Paroxymsal nocturnal hemoglobinuria = acquired PIG-A mutation –> impaired GPI anchor synthesis for CD55 and CD59 (which protect RBC membrane from complement) –> complement mediated intravascular hemolysis
List 6 major pathophysiologic processes that contribute to vaso-occlusion in sickle cell disease
- Inflammation
- Leukocyte / platelet activation
- Nitric oxide dysregulation
- Endothelial dysfunction
- Hypercoagulability
- Oxidative stress from reperfusion injury
What is the difference in the management of Rh hemolytic disease and ABO hemolytic disease of the newborn?
-
Rh hemolytic disease
- Give anti-D immune globulin to Rh negative pregnant women during all pregnancies, in 3rd trimester, and any time there may be maternal-fetal bood exchange (goal is to prevent mom from developing antibodies; if she has them, goal is to prevent antibodies from killing the baby)
-
ABO hemolytic disease
- Transfusions in utero before delivery, if there is evidence of hemolysis
- ABO heomlytic disease is more common, but less serious than Rh hemolytic disease
Describe the pathophysiology of hereditary spherocytosis (spherocyte formation)
2 possible pathways, depending on which protein is mutated
Spectrin or ankyrin deficiency -> Unsupported membrane
OR
Band 3 deficiency -> Clustered lipids in the phospholipid membrane
Both result in budding off of membrane parts -> spherocyte formation
What test is used to confirm diagnosis of hereditary spherocytosis?
Osmotic fragility testing
- RBCs cannot accomodate swelling in hyposmotic solutions; they just pop :(
List the 2 primary structural components that make up the RBC membrane
- Lipid bilayer
- Network of skeletal and transmembrane proteins
What defines acute chest syndrome in a patient with sickle cell disease? (3)
Fever + Abnormal chest X-ray + Any respiratory sign/sx
- Etiology is multifactorial
- Infection, pulmonary infarction, fat emboli
- Often preceded by pain episode
What is actually happening in a red blood cell when it sickles?
What is the major trigger for sickling?
Hb Polymerization -> sickling
Occurs during deoxygenation
Sickling may be exacerbated by:
- Increased HbS concentration
- More acidic pH
- Cation homeostasis: activation of the KCl cotransporter
- Dehydration
What is the major complication that results from Paroxysmal nocturnal hemoglobinuria?
Thrombis, especially in unusual sites
- Portal vein
- Cerebral vessels
- Cutaneous veins
Results from complemented-mediated destruction of RBCs -> membranes in the circulation -> clots
What does the Direct Coombs Test detect?
How does it work?
Detects auto-antibody or complement directly bound to patient’s RBCs
- Take pt’s RBCs, add standard antiglobulin (ex: anti-IgG, anti-IgM, anti-complement, or a mix) (these are antibodies against the antibodies that bind to the RBCs)
- Look to see if these antiglobulins (anti-antibodies) bind to the pt’s RBCs (clumping)
- If so, they are boud to IgG, IgM, or complement (depending on the antiglobulin used)
Usually do all anti-globulins together, and then if positive do them individually
Indirect Coombs takes normal RBCs and mixes with pt plasma, detects both autoantibodies and alloantibodies in the plasma
Describe the mutation and resulting amino acid substitution that causes sickle hemoglobin
A -> T in the 6th codon of the beta-globin gene
Results in glutamic acid -> valine substitution
How will the following change in hemolytic anemia?
- Reticulocytes:
- Haptoglobin:
- Bilirubin:
- LDH:
Hemolytic anemia
- Reticulocytes: Increased (trying to replace decreased RBCs)
- Haptoglobin: Decreased (haptoglobin binds to free Hb from lysed RBCs, then cleared by phagocytes)
- BIlirubin: Increased indirect (excess bilirubin from heme breakdown is unconjugated)
- LDH: Increased (released by damaged RBCs, but not specific to hemolysis)
Differences in amt of change in extravascular vs. intravascular
What red blood cell morphology will result from pyruvate kinase deficiency?
Echinocytes (Burr cells)
Describe the pathophysiology of cold antibody hemolytic anemia
Cold agglutinin antibodies (usually IgM) interact with polysaccharides on the RBC surface
hemolysis is then due to complement formation
List 2 scenarios in which 46,XX individuals who are heterozygous for G6PD deficiency will be symptomatic
- X chromoxome inactivation
- Skewed lyonization (skewed X chromosome inactivation)
What does the Indirect Coombs Test detect?
How does it work?
Can find both autoantibodies and alloantibodies in the patient’s plasma
Pts may have developed antobodies to previously transfused blood
- Mix normal RBCs with patient’s plasma
- If binding occurs, implies that there are antibodies in the plasma
vs. Direct coombs measures antibodies that are bound to RBCs, can only detect autoantibodies
What is the mechanism of action of hemolysis in G6PD deficiency?
No G6PD -> cannot make NADPH -> cannot reduce glutathione
-> cannot deal with oxidative stress
Oxidative stress -> hemoglobin denatures -> hemolysis
Will see Heinz bodies and Bite Cells (degmacytes) in RBCs
