Anemia IV - Hemolytic Anemias Flashcards
Why is the RBC uniquely susceptible to stressors?
- Lacks a nucleus
- Cannot synthesize protein (except reticulocyte)
- Must rely on its content of vital proteins to last its lifetime -> any change in environment can damage it
What are the classifications of hemolytic anemia by site?
Extravascular - i.e. splenic removal
Intravascular - i.e. shear forces or autoimmunity
What are the classifications of hemolytic anemia by mechanism? How are they usually acquired? Give examples of them.
Intrinsic - usually genetic
Examples: G6PDH deficiency, hemoglobinopathies, PNH (actually acquired)
Extrinsic - usually acquired
Immune-mediated, microangiopathic, mechanical trauma-mediated
Do extravascular hemolytic anemias usually cause iron deficiency? Why or why not?
Usually not, because all components of the RBC are rapidly recycled via the RES.
i.e. globins returned to amino acid pool, heme made into unconjugated bilirubin and conjugated / recycled by liver, and IRON moved back into storage pool
Why is intravascular hemolysis more dangerous than extravascular?
Intravascular hemolysis leads to a dumping of a large amount of hemoglobin into the blood.
Some of that is scavenged by haptoglobin or albumin (makes methhemalbumin), but a large portion ends up in the kidneys causing hemoglobinuria / hemosiderinuria which is very damaging
Describe the clinical pictures of extravascular and intravascular hemolysis and give an example of each.
Extravascular - insidious onset with gradual icterus and pallor, i.e. hereditary spherocytosis
Intravascular - rapid onset with sudden icterus and pallor, fulminant course, i.e. PNH
What are general clinical findings of all hemolytic anemias?
Pallor, fatigue, jaundice, dark urine (hemoglobin), gallstones (bilirubin), aplastic crises with viral infections
What is hereditary spherocytosis a prototype of? What causes it?
Extravascular, intrinsic hemolysis
RBC cytoskeleton-membrane tethering proteins such as spectrin, ankyrin, or Band 3.
Vertical interactions cause blebbing of membrane and sphering outward. Horizontal interactions prevent forming of spectrin tetramers which make membrane unstable -> eaten in chunks by splenic macrophages
How can you tell a spherocyte on peripheral blood smear and why do they get eaten by the spleen? What will happen to the reticulocyte count?
Have no area of central pallor (not biconcave), get eaten because they don’t fight properly through splenic sinusoids
Reticulocyte count will also be elevated
What first test is used to diagnose spherocytosis?
Osmotic fragility test. Normal saline is ~0.9% sodium chloride. If you spherocytes, lysis will begin at an early point in hypotonic saline solution (spherocytes have less volume to swell than regular RBCs)
-> right shifted curve, cannot handle osmotic stress as well
What is the confirmatory test used to diagnose spherocytosis?
Eosin-maleimide (EMA) binding by flow. Spherocytosis will bind less EMA.
What is the inheritance pattern of hereditary spherocytosis?
Autosomal dominant with weak penetrance
How is spherocytosis managed?
Establish a steady state Hb to monitor for aplastic crises, anticipate gallstones, and give splenectomy for selected patients
Why is splenectomy effective for spherocytosis and what will be seen on peripheral blood smear?
Removes the site of extravascular hemolysis
Peripheral smear -> spherocytes persist, and Howell-Jolly bodies appear (fragments of nuclear material in RBCs which spleen normally removes)
What does the Embden-Meyerhoff pathway produce?
Another name for glycolysis, produces 2 ATP per 1 glucose
What does the Rappoport shunt produce?
2,3 DPG
Uses a mutase to make 1,3-DPG into 2,3-DPG, which is needed for RBC oxygen transport
Why is the hexose monophosphate shunt important for RBCs? What commonly upsets this?
G6PDH keeps glutathione in its reduced form so it can reduce oxidative stressors (including hydrogen peroxide and hydroxyl radical) back to water.
X-linked recessive mutations in G6PDH prevent formation of NADPH
What is the carrier frequency of G6PDH and why? What are the two variants?
Around 10%, offers protection against falciparum malaria
African variant - mildly reduced G6PDH halflife, less severe form
Mediterranean / Caucasian variant - significantly reduced halflife, chronic hemolytic anemia which may be transfusion dependent
What do cells look like on peripheral blood smear of G6PD? How are they seen on a special stain?
Mothball cells - look like a hanging basket, dense hemoglobin aggregates on one side of the cell, opposite side will be relatively clear
Associated with formation of Heinz bodies (visualized by special stain) which are removed by splenic macrophages to make bite cells (probably the same as mothball cells)
What things precipitate hemolysis in G6PD deficiency? is this intravascular or extravascular?
Predominantly intravascular hemolysis, so will cause kidney damage (no splenomegaly)
Antimalarials (i.e. primaquine), slufa drugs, nitrofurantoin, Fava beans, naphthelene (mothballs), overwhelming infections
What causes Paroxysmal Nocturnal Hemoglobinuria?
Acquired defect in glycosylphosphatidylinositol (GPI) gene within myeloid stem cells
-> lack of GPI anchor prevents expression of decay-accelerating factor (CD55) and CD59, which are needed to inhibit C3 convertase and thus fixation of complement
What is the primary clinical problem in PNH?
Thrombosis of hepatic, portal, and cerebral veins since platelets will also lack CD55 and thus be activated to form clots
Other than thrombosis, what other problems plague PNH patients? One of these things is a cancer.
Hemosiderinuria - and thus chronic iron deficiency due to loss of iron in urine
Progression to aplastic anemia and acute myeloid leukemia (AML)
-> think that other oncogenes can develop in that stem cell
How is the diagnosis of PNH made? What is the treatment?
Usually by flow cytometry showing lack of CD55/CD59
Treatment: Bone marrow transplant, immunosuppression, and eculizumab (C5 complement inhibitor, prevents formation of MAC)
What is an excellent prototype of extravascular, extrinsic hemolysis? How does it work?
Auto-immune hemolytic anemia (AIHA)
Antibody coats RBC, and defective RBC is removed by spleen
What causes warm reactive AIHA? What type of antibodies are they?
Usually associated with SLE, often idiopathic
IgG or complement specific antibodies active at 37 degrees Celsius in warm temperatures of body
What causes cold reactive AIHA? What type of antibodies are they?
IgM antibodies usually active at 2 to 4 degrees C in the lab, works more in cold temperatures of extremities
Antibodies (cold agglutinins) made in lymphoma, infectious mononucleosis, and Mycoplasma pneumoniae
What is Evan’s syndrome?
When autoimmune hemolytic anemia also associated with attacking platelets
-> causes mild thrombocytopenia not associated with bleeding
What test is usually positive in autoimmune hemolytic anemias? How does it work?
Direct Coombs test
- > remove blood from patient’s body, wash RBCs
- > If autoantibodies are present, antibodies will continue sticking to RBCs
- > adding Coombs reagent (anti-human Ig) will cause agglutination in a positive test
What is an indirect Coombs test? and why would it be needed?
Take human type O red cells, add patient’s serum. If antibodies are present to donor RBCs, adding the Coombs reagent (anti-human Ig) will cause agglutination of RBCs
Why would an indirect Coombs test be needed?
Needed when antibody titers are too low to sensitize RBCs directly (less severe hemolytic disease, not strong enough to show direct RBC agglutination by direct Coombs)
How is AIHA managed?
Keep hemoglobin at safe levels (>4 g/dL) with transfusions
High dose steroids - prevent Ab production
Alkalize urine to protect kidneys
Plasmapheresis - strain out Abs
Splenectomy
Why is splenectomy useful in AIHA?
Especially useful with IgG mediated disease (warm agglutinins), which mainly acts as an opsonin for splenic macrophages
- Removal of spleen removes major site of antibody production
- Removal of spleen prevents filtering of blood by splenic macrophages
What is allo-immune “minor” blood antigen mismatch?
Minor Rh antigens which you are negative for but are present in donor blood cause no problem the first time, but you develop antibodies against them
Next time you receive that blood you have a hemolytic anemia from donor blood
What is drug induced antibody hemolysis?
Very similar to warm agglutinin IgG-mediated disease, happens in one of two ways.
- Antibody is formed to drug-RBC membrane complex (i.e. penicillin)
- Antibody is formed to RBC membrane due to presence of drug, hemolytic anemia persists in absence of drug (i.e. a-methyldopa)
What is microangiopathic anemia and what are some causes?
Intravascular hemolysis caused by vascular pathology, and RBCs are destroyed as they pass through circulation
Microthrombi states (TTP/HUS), DIC, SLE, HELLP (hemolysis, elevated liver enzymes, low platelets)
What is seen on peripheral smear in microangiopathic anemia?
Schistocytes -> due to mechanical destruction of RBCs as they are sheared by fibrin
Looks like a helmet
What are common causes of macroangiopathic anemia? What will be seen on blood smear?
Prosthetic heart valves, aortic stenosis, or arterial grafts
-> mechanical destruction of RBCs with Schistocytes on peripheral smear.
What is March hemoglobinuria?
Repeated physical trauma to red cells during jogging, marching, karate, etc causes an intravascular hemolysis (trauma while in vessels of feet)
When do you test for a G6PD deficiency?
Wait til the acute attack is over -> need RBCs to be regenerated to check for enzyme levels. If you check during acute attack, only cells with adequate G6PD will be sampled.
