Hematology Exam 8 (RBC defects) Flashcards
Acute vs chronic hemolytic anemia
Acute: rapid onset, isolated/episodic (ex. PCH, PNH, hemolytic TRXN)
Chronic: may not be evident if BM is able to compensate, but becomes evident if hemolytic crises occur that cause anemia (ex. G6PD, thalassemia)
Inherited vs acquired hemolytic anemia
Inherited: passed to offspring (ex. thalassemia)
Acquired: develop in patients who acquire a condition that lyses RBC (ex. malaria)
Intrinsic vs extrinsic hemolytic anemia
Intrinsic: the defect is in the RBC
Extrinsic: the defect is outside the RBC such as in the plasma
What is another name for intravascular hemolysis?
Fragmentation hemolysis
What is another name for extravascular hemolysis?
Macrophage-mediated hemolysis
What is the “normal” type of hemolysis?
Extravascular hemolysis
What type of hemolysis accounts for 80-90% of normal hemolysis?
Extravascular hemolysis
What is the normal cause of extravascular hemolysis?
Macrophages of the spleen and liver recognize old RBCs and phagocytize them
What type of hemolysis accounts for 10-20% of normal hemolysis?
Intravascular hemolysis
What is the cause of intravascular hemolysis?
Result of trauma to RBC membrane that causes cell contents such as hemoglobin to spill directly into the plasma
What type of hemolysis activates the haptoglobin-hemopexin-methemalbumin system?
Intravascular hemolysis
What lab values are seen with excessive extravascular hemolysis?
Increased bilirubin
Increased urobilinogen in urine
What lab values are seen with excessive intravascular hemolysis?
Hemoglobinemia
Hemoglobinuria
Hemosiderinuria
Decreased haptoglobin
Decreased hemopexin
Increased bilirubin
What is excessive intravascular hemolysis characterized by?
Appearance of the contents of RBCs into the plasma (especially hemoglobin) – hemoglobinemia
What cells in the peripheral smear are seen with extravascular hemolysis? Intravascular hemolysis?
Spherocytes - extravascular
Schistocytes - intravascular
What tests can be run to determine accelerated RBC destruction?
Bilirubin, plasma hemoglobin, urine hemoglobin, urine hemosiderin, CBC, haptoglobin and hemopexin, carbon monoxide, lactate dehydrogenase
What is the most common test of increased erythropoiesis
Reticulocyte count
What is meant by tests of increased erythropoiesis?
Tests that indicate that the bone marrow is trying to compensate for anemia; such as increased retics/nRBCs or changes in the CBC and bone marrow
What do increased results for tests of increased erythropoiesis indicate?
That the BM is trying to compensate for anemia by the presence of immature RBCs
List and briefly describe 3 properties enabling RBC deformability. Why is it important for RBCs to be deformable?
- biconcave shape - allow for vertical/horizontal interactions
- membrane elasticity - allow for movement of membrane
- cytoplasmic viscosity - allows the function of pumps and channels
What are vertical interactions in the RBC membrane
Interactions between the membrane and the cytoskeleton (ankyrin and actin of the membrane interact with spectrin of the cytoplasm)
What are horizontal interactions in the RBC membrane?
Prevents the membrane from fragmenting in response to mechanical stress (within one layer, membrane only interactions or cytoskeleton only interactions)
What are the standout features of hereditary spherocytosis?
- vertical interactions
- decreased surface area to volume ratio
- increased MCHC >36
- increased osmotic fragility
- spherocytes seen in peripheral smear
- anemia, jaundice, splenomegaly
What test can be done to determine if someone has hereditary spherocytosis?
Osmotic fragility test (blood added to series of tubes with increasingly hypotonic saline solutions, those with HS will hemolyze in lower concentrations due to increased osmotic fragility of spherocytes)
What are the results of the following tests in a patient with hereditary spherocytosis (HS)?
- osmotic fragility
- MCHC
- peripheral smear
- membrane to surface area ratio
osmotic fragility = increased
MCHC = increased
peripheral smear = spherocytes
membrane to surface area ratio = decreased
Standout features of hereditary elliptocytosis
- horizontal interactions
- elliptical/cigar shaped RBCs in smear
Standout features of hereditary pyropoikilocytosis
- subtype of HE
- cells have thermal sensitivity
- very low MCV
- extreme poikilocytosis with elliptocytes
Standout features of hereditary ovalocytosis
- increased rigidity of membrane
- resistance to invasion by malaria
- oval RBCs with one to two transverse bars or ridges
- caused by a mutation that deletes 9 amino acids in band 3
What are the 6 hereditary RBC membrane abnormalities?
ALTER MEMBRANE STRUCTURE:
hereditary spherocytosis
hereditary pyropoikilocytosis
hereditary elliptocytosis
hereditary ovalocytosis
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ALTER MEMBRANE TRANSPORT PROTEINS:
overhydrated hereditary stomatocytosis
dehydrated hereditary stomatocytosis
What cells are seen in increased cation content of RBCS?
stomatocyte (aka overhydrated hereditary stomatocytosis)
What cells are seen in decreased cation content of RBCS?
xerocyte (aka dehydrated hereditary stomatocytosis)
Another name for DHS?
xerocytosis
Another name for OHS?
hydrocytosis
Standout features of overhydrated hereditary stomatocytosis (hydrocytosis)
- RBCs overhydrated
- membrane excessively permeable to sodium and potassium (water enters cell)
- increased cation content
- stomatocytes
Standout features of dehydrated hereditary stomatocytosis (xerocytosis)
- RBCs dehydrated
- membrane excessively permeable to potassium (water exits cell)
- decreased cation content
- xerocytes/stomatocytes
What does it mean for an RBC to have a decreased surface area to volume ratio? What does it mean for an RBC to have increased osmotic fragility?
Decreased surface area to volume ratio making them lyse more easily which make them more susceptible to lysis by water entering the cell aka increased osmotic fragility
What are two disorders that result from mutations that alter membrane transport proteins? What are differences between these two disorders?
OHS and DHS
OHS has increased cation content of the cell and cell is overhydrated and permeable to both sodium and potassium
DHS has decreased cation content of the cell and cell is dehydrated and permeable to only potassium
They both lead to stomatocytes
What is the cause of spur cell anemia?
Excess free cholesterol that accumulates on outer layer of RBC membrane forming acanthocytes
What is PNH (paroxysmal nocturnal hemoglobinuria)?
Mutation of PIGA gene, results in absence of CD55 and CD59 from RBC membrane, leads to cell being more susceptible to lysis by complement
Clinical manifestations of PNH
Dark urine (hemoglobinuria)
Evidence of intravascular hemolysis
Iron deficiency can develop
Negative DAT
How to test for PNH?
Flow cytometry, detection of normal/lack of/absence of CD59 markers on RBC
The more type III cells (no CD59), the more severe the hemolysis
Detecting absence/presence of GPI-anchored proteins on WBCs using flow cytometry
Treatment for PNH
Eculizumab (prevents formation of MAC)
What RBC metabolic pathway is affected by G6PD deficiency and what is the result for the RBC?
- Affects hexose monophosphate shunt
- RBCs vulnerable to oxidative damage and subsequent hemolysis during oxidant stress
What is the most common RBC enzyme defect?
G6PD deficiency
What is seen in RBC morphology of those with G6PD deficiency?
Heinz bodies (made of denatured hemoglobin)
What population has the highest prevalence of G6PD deficiency?
Malaria endemic areas
Clinical manifestations of G6PD deficiency
Most patients are asymptomatic
Can lead to acute hemolytic anemia, neonatal jaundice, HNSHA
What disease discussed can be triggered by the ingestion of fava beans?
G6PD deficiency
What is the most common cause of a hemolytic episode in G6PD deficient patients?
Infection (bacteria, viruses, rickettsia)
Favism
rare, severe hemolytic episode seen in G6PD deficient patients after ingestion of fava beans
- more common in G6PD mediterranean variant
How does a G6PD deficiency lead to oxidative damage in the RBC?
Lack of G6PD = not making NADH, cannot reduce glutathione in hexose monophosphate shunt, cannot detoxify hydrogen peroxide –> oxidative damage
What are heinz bodies?
Precipitated denatured hemoglobin
What is the gold standard to test for G6PD deficiency?
Quantitative spectrophotometric assays, direct measurement of NADPH generated (decreased G6PD = decreased NADPH = less fluorescence)
What RBC metabolic pathway is affected by PK deficiency? What is the result for RBC affected?
Glycolytic pathway (Ebden-Meyerhoff)
Causes a depletion of ATP leading to a right shift (increased 2,3-BPG, release oxygen to tissues, patient can tolerate lower HGB levels)
What population is more affected by PK deficiencies?
Two consanguineous communities in the US: Amish families in PA
Children from polygamist families in a small town in the midwest
Clinical manifestations of PK deficiency?
Episodes of chronic hemolysis
Increased risk of iron overload with age
Tests for PK deficiency (how does this test differ from the test for G6PD deficiency)
Quantitative PK assay, measures rate of NAD formation proportional to PK activity (fluorescence = PK deficiency)
The difference between these tests is fluorescence for PK = deficiency
LACK of fluorescence for G6PD = deficiency
What are MAHAs? What are some notable findings in all MAHAs?
MAHAs are extrinsic RBC defects (non immune) and stand for microangiopathic hemolytic anemias. They are all characterized by RBC fragmentation and thrombocytopenia
Laboratory values for MAHAs
Decreased HGB
Increased retics
Increased bilirubin
Increased LDH
Decreased haptoglobin
Increased urine urobilinogen
Schistocytes
Thromobocytopenia
What are the 4 MAHAs discussed?
TTP
HUS
DIC
HELLP
What is TTP characterized by? What differentiates TTP from DIC?
deficiency of enzyme ADAMTS13
TTP has normal coag results
What is atypical AND typical HUS characterized by?
Typical HUS - caused by bacteria that produce Shiga-like toxin 1 (STEC)
Atypical HUS - unregulated activation of alternative complement pathway
PLTs only mildly decreased, renal failure is present
What is HELLP syndrome characterized by? How is this differentiated from DIC?
Hemolysis, elevated liver enzymes, low platelet count
Coagulation results are normal
What is major diagnostic criteria for HELLP syndrome?
Elevated LDH and AST with low PLT count
What is DIC characterized by?
Increased D dimer
Decreased fibrinogen
Prolonged PT and PTT
This distinguishes DIC from other MAHAs (coag results abnormal)
What is a consistent finding in the peripheral smear for ALL MAHAs?
Schistocytes
Treatment for TTP
Plasma exchange therapy
Treatment for atypical HUS
Eculizumab (antibody to C5)
What is the mechanism of hemolytic anemia caused by malaria?
Malaria parasites metabolize hemoglobin forming toxic hemozoin which results in inhibition of erythropoiesis and decreased iron availability
What is the mechanism of hemolytic anemia caused by babesiosis?
Transmitted through tick caused by bacteria B. microti
What is the mechanism of hemolytic anemia caused by clostridial sepsis?
complication of C. perfringens infection, alpha-toxin hydrolyzes RBC membrane phospholipids and RBCs become spherical and susceptible to osmotic lysis
What is the mechanism of hemolytic anemia caused by bartonellosis?
Transmitted through bite of female sandfly, B. bacilliformis adheres to RBCs and causes hemolysis and produces deformin which forms pits in RBC membrane
Other nonimmune causes of hemolytic anemias
Drugs/chemicals (dapsone, naphthalene (mothballs), arsine hydride, copper, lead)
Venoms from snakes/spiders/bees/wasps
Extensive burns
Define immune hemolytic anemias
Conditions with shortened RBC survival due to antibody-related mechanisms
What are the 3 major classifications of immune hemolytic anemias?
Autoimmune hemolytic anemia
Alloimmune hemolytic anemia
Drug induced immune hemolytic anemia
How does IgM mediated hemolysis differ from IgG mediated hemolysis?
IgM mediated hemolysis: requires complement, can result in both extra and intravascular hemolysis
IgG mediated hemolysis: occurs with or w/o complement, results predominantly in extravascular hemolysis
**IgM more efficient at activating complement than IgG
What is the purpose of the DAT? Why is it relevant to immune hemolytic anemias?
Detects in vivo sensitization of RBC surface by IgG or C3. It is relevant because this occurs during IHAs.
What are the 4 categories of autoimmune hemolytic anemias?
WAIHA, CAD, PCH, mixed-type
WAIHA - antibodies involved, test results
React at 37C and are IgG
Most common AIHA
Usually panreactive
Positive DAT (IgG)
Lab findings reflect extravascular hemolysis
CAD - antibodies involved, test results
React at 4C and are IgM
Most often anti-I
Positive DAT (C3)
Lab findings reflect extravascular hemolysis
Falsely increases MCHC, MCV, and falsely reduces RBC count
PCH - antibodies involved, test results
Anti-P aka Donath Landsteiner antibody
Biphasic - partially activates complement at cold temperatures and when warmed fully activates complement
Intravascular hemolysis
Positive DAT (C3)
What AIHA is biphasic?
PCH - Donath Landsteiner Antibody
Mixed type AIHA
Both WAIHA and CAD, extra and intravascular hemolysis, positive DAT
Acute vs chronic hemolytic transfusion reactions
Acute - occur within minutes, most common cause is ABO incompatible cells, intravascular
Chronic - occur within days/weeks, most common cause is Duffy/Kidd, extravascular
Rh HDFN
Most severe form of HDFN, mom has anti-D, baby is rH positive, antibodies sensitize fetal cells and cause anemia/hyperbilirubinemia/extravascular hemolysis
Which is the most common HDFN? Which is the most severe?
Most common: ABO
Most severe: Rh
Mechanisms of drug-induced immune hemolysis: Drug adsorption
Patient produces IgG antibody to a drug, binds to the drug, extravascular hemolysis
Mechanisms of drug-induced immune hemolysis: Drug-RBC membrane protein immunogenic complex
Drug binds RBC membrane protein and forms a complex/epitope, patient produces antibody to the complex, antibody binds and activates complement causing intravascular hemolysis
Mechanisms of drug-induced immune hemolysis: RBC autoantibody induction
Drug induces patient to make IgG autoantibodies against self-antigens –> extravascular hemolysis
Autoimmune vs alloimmune hemolytic anemias
Autoimmune - caused by self antibodies
Alloimmune - caused by non self antibodies
Which protein binds heme released into plasma during intravascular hemolysis?
Hemopexin
