Anemia IV - Hemolytic Anemias

Question 1

Why is the RBC uniquely susceptible to stressors?

Answer 1

1. Lacks a nucleus
2. Cannot synthesize protein (except reticulocyte)
3. Must rely on its content of vital proteins to last its lifetime -> any change in environment can damage it

Question 2

What are the classifications of hemolytic anemia by site?

Answer 2

Extravascular - i.e. splenic removal

Intravascular - i.e. shear forces or autoimmunity

Question 3

What are the classifications of hemolytic anemia by mechanism? How are they usually acquired? Give examples of them.

Answer 3

Intrinsic - usually genetic
Examples: G6PDH deficiency, hemoglobinopathies, PNH (actually acquired)

Extrinsic - usually acquired
Immune-mediated, microangiopathic, mechanical trauma-mediated

Question 4

Do extravascular hemolytic anemias usually cause iron deficiency? Why or why not?

Answer 4

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

Question 5

Why is intravascular hemolysis more dangerous than extravascular?

Answer 5

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

Question 6

Describe the clinical pictures of extravascular and intravascular hemolysis and give an example of each.

Answer 6

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

Question 7

What are general clinical findings of all hemolytic anemias?

Answer 7

Pallor, fatigue, jaundice, dark urine (hemoglobin), gallstones (bilirubin), aplastic crises with viral infections

Question 8

What is hereditary spherocytosis a prototype of? What causes it?

Answer 8

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

Question 9

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?

Answer 9

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

Question 10

What first test is used to diagnose spherocytosis?

Answer 10

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

Question 11

What is the confirmatory test used to diagnose spherocytosis?

Answer 11

Eosin-maleimide (EMA) binding by flow. Spherocytosis will bind less EMA.

Question 12

What is the inheritance pattern of hereditary spherocytosis?

Answer 12

Autosomal dominant with weak penetrance

Question 13

How is spherocytosis managed?

Answer 13

Establish a steady state Hb to monitor for aplastic crises, anticipate gallstones, and give splenectomy for selected patients

Question 14

Why is splenectomy effective for spherocytosis and what will be seen on peripheral blood smear?

Answer 14

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)

Question 15

What does the Embden-Meyerhoff pathway produce?

Answer 15

Another name for glycolysis, produces 2 ATP per 1 glucose

Question 16

What does the Rappoport shunt produce?

Answer 16

2,3 DPG

Uses a mutase to make 1,3-DPG into 2,3-DPG, which is needed for RBC oxygen transport

Question 17

Why is the hexose monophosphate shunt important for RBCs? What commonly upsets this?

Answer 17

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

Question 18

What is the carrier frequency of G6PDH and why? What are the two variants?

Answer 18

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

Question 19

What do cells look like on peripheral blood smear of G6PD? How are they seen on a special stain?

Answer 19

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)

Question 20

What things precipitate hemolysis in G6PD deficiency? is this intravascular or extravascular?

Answer 20

Predominantly intravascular hemolysis, so will cause kidney damage (no splenomegaly)

Antimalarials (i.e. primaquine), slufa drugs, nitrofurantoin, Fava beans, naphthelene (mothballs), overwhelming infections

Question 21

What causes Paroxysmal Nocturnal Hemoglobinuria?

Answer 21

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

Question 22

What is the primary clinical problem in PNH?

Answer 22

Thrombosis of hepatic, portal, and cerebral veins since platelets will also lack CD55 and thus be activated to form clots

Question 23

Other than thrombosis, what other problems plague PNH patients? One of these things is a cancer.

Answer 23

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

Question 24

How is the diagnosis of PNH made? What is the treatment?

Answer 24

Usually by flow cytometry showing lack of CD55/CD59

Treatment: Bone marrow transplant, immunosuppression, and eculizumab (C5 complement inhibitor, prevents formation of MAC)

Question 25

What is an excellent prototype of extravascular, extrinsic hemolysis? How does it work?

Answer 25

Auto-immune hemolytic anemia (AIHA)

Antibody coats RBC, and defective RBC is removed by spleen

Question 26

What causes warm reactive AIHA? What type of antibodies are they?

Answer 26

Usually associated with SLE, often idiopathic

IgG or complement specific antibodies active at 37 degrees Celsius in warm temperatures of body

Question 27

What causes cold reactive AIHA? What type of antibodies are they?

Answer 27

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

Question 28

What is Evan’s syndrome?

Answer 28

When autoimmune hemolytic anemia also associated with attacking platelets
-> causes mild thrombocytopenia not associated with bleeding

Question 29

What test is usually positive in autoimmune hemolytic anemias? How does it work?

Answer 29

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

Question 30

What is an indirect Coombs test? and why would it be needed?

Answer 30

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

Question 31

Why would an indirect Coombs test be needed?

Answer 31

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)

Question 32

How is AIHA managed?

Answer 32

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

Question 33

Why is splenectomy useful in AIHA?

Answer 33

Especially useful with IgG mediated disease (warm agglutinins), which mainly acts as an opsonin for splenic macrophages

1. Removal of spleen removes major site of antibody production
2. Removal of spleen prevents filtering of blood by splenic macrophages

Question 34

What is allo-immune “minor” blood antigen mismatch?

Answer 34

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

Question 35

What is drug induced antibody hemolysis?

Answer 35

Very similar to warm agglutinin IgG-mediated disease, happens in one of two ways.

1. Antibody is formed to drug-RBC membrane complex (i.e. penicillin)
2. Antibody is formed to RBC membrane due to presence of drug, hemolytic anemia persists in absence of drug (i.e. a-methyldopa)

Question 36

What is microangiopathic anemia and what are some causes?

Answer 36

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)

Question 37

What is seen on peripheral smear in microangiopathic anemia?

Answer 37

Schistocytes -> due to mechanical destruction of RBCs as they are sheared by fibrin

Looks like a helmet

Question 38

What are common causes of macroangiopathic anemia? What will be seen on blood smear?

Answer 38

Prosthetic heart valves, aortic stenosis, or arterial grafts

-> mechanical destruction of RBCs with Schistocytes on peripheral smear.

Question 39

What is March hemoglobinuria?

Answer 39

Repeated physical trauma to red cells during jogging, marching, karate, etc causes an intravascular hemolysis (trauma while in vessels of feet)

Question 40

When do you test for a G6PD deficiency?

Answer 40

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.