Hemolytic Anemias Flashcards
(51 cards)
Primary building blocks of the RBC membrane
α-spectrin and β-spectrin, which bind to each other to form long, stable dimers
protein 4.1 facilitates their association with actin
band 3, ankyrin, and protein 4.2 help the skeleton stay connected to the membrane.
Red cell membrane cross section
Defects in horizontal red cell membrane interactions cause ___.
hereditary elliptocytosis or its severe variant, hereditary pyropoikilocytosis
Defects in vertical red cell membrane interactions cause ___.
hereditary spherocytosis
Osmotic fragility test
Lab test that provides an assessment of the surface area to volume ratio of red cells. Basically dilute the concentration of salt until the cells pop, which you can detect by measuring hemoglobin release.
Cells with a low vs high surface area to volume ratio
Spherocytes have a low SA:V, and so they will pop quickly in an osmotic fragility test
Target cells have a high SA:V ratio, so they will take longer than healthy red cells to pop
Mutations that cause hereditary spherocytosis
Ankyrin
band 3
β-spectrin
protein 4.2 (this one causes a mild spherocytosis)
Many individuals with uncomplicated hereditary spherocytosis are asymptomatic. Why is this?
They can compensate with constantly elevated erythrocyte production. This is “compensated” hemolytic anemia.
Of course, if they are to be, say, infected with parvovirus B19, they will have a much worse disease than an individual with normal erythrocytes.
Clinical features of hereditary spherocytosis
- Splenomegaly
- Increased retics
- Markers of intravascular hemolysis + associated (icterus, gall stones, etc)
*
While spherocytes on blood smear certainly put hereditary spherocytosis on the differential, . . .
. . . multiple things can cause spherocytosis. Immune hemolytic anemia also produces spherocytosis. It takes an osmotic fragility test or genetic test to confirm the diagnosis.
What is the likely diagnosis?
Hereditary spherocytosis
___ is recommended in all patients with severe hereditary spherocytosis.
Splenectomy is recommended in all patients with severe hereditary spherocytosis.
However, you may want to wait until patients are at least >3 years old for immune system development, and for all necessary vaccinations.
Partial splenectomy is currently gaining favor.
Hereditary elliptocytosis mutations
α-spectrin
β-spectrin
protein 4.1
Hereditary elliptocytosis
Defect in the horizontal interactions prevents stable hexagonal αβ-spectrin arrangement, resulting in elliptical red cells.
Often results in only a modest anemia or no anemia at all. However, a small portion of these individuals have severe anemia (poikilocytosis) from birth. This will typically evolve into a mild anemia within a year.
Fewer still (often compound heterozygotes) have hereditary pyropoikilocytosis, a severe congenital anemia that does not improve and is transfusion dependent.
What is the likely diagnosis?
Hereditary elliptocytosis
Hereditary xerocytosis
Red cells are severely dehydrated due to defects in the control of red cell cation content that result in potassium efflux.
Osmotic fragility test shows high SA:V ratio, more like targetoid cells than spherocytes. Target cells may sometimes be seen, but overall morphology on smear is normal. However, cells are rigid and rapidly cleared by the spleen.
High risk for thromboembolism after splenectomy.
Hereditary stomatocytosis
Red cells are overhydrated owing to excess influx of sodium and water.
Stomatocytes have a mouth-like slit rather than a circular area of central pallor.
High risk for thromboembolism after splenectomy.
Why is splenectomy avoided in hereditary xerocytosis and stomatocytosis?
Because it results in a high risk of thromboembolism, possible due to accumulation of damaged erythrocytes that may serve as thrombus nucleation sites.
What is the likely diagnosis?
Hereditary stomatocytosis
What’s wrong with these red cells?
Their hemoglobin has precipitated out of solution to form Heinz bodies. This is the result of oxidative stress that is uncompensated for by red cell redox buffers, like glutathione.
Glucose-6-phosphate dehydrogenase deficiency
The enzyme that is necessary to commit glucose to the pentose phosphate pathway. Without it, red cells cannot produce NADPH to recharge their glutathione stores and are prone to oxidative stress.
G6PDH is on the X chromosome, so the deficiency is X-linked.
With the exception of the rare disorder paroxysmal nocturnal hemoglobinuria, all of the acquired hemolytic anemias are ___
With the exception of the rare disorder paroxysmal nocturnal hemoglobinuria, all of the acquired hemolytic anemias are extracorpuscular
This means that red cells from a compatible donor are hemolyzed as readily as the patient’s own red cells.
Warm autoantibodies
Bind avidly to the patient’s red cells at body temperature. They are immunoglobulin G (IgG) antibodies with specificity for Rh group antigens found on red cells of nearly all individuals.
How spherocytes form due to immune reactions against blood cells.
IgG binds Rh factor on an erythrocyte. A macrophage binds via an Fc gamma receptor. Often, erythrocytes are completely eaten, but sometimes they are able to get away after being ‘nibbled on’ by the macrophage. This results in a loss of extra surface area, and thus the cell takes on the morphology of a spherocyte.
