RBC metabolism and Disorders Flashcards
1
Q
What do RBC’s need energy for maintaining?
A
High intracellular K+, low Na+, and very low Ca++
Hgb in reduced form
High levels of reduced glutathione
Membrane integrity and deformability
2
Q
What pathway is 90-95% of the glucose consumption utilized by?
A
Embden-Meyerhof pathway
3
Q
What are the products of the Embden-Meyerhof pathway?
A
Glucose is metabolized to lactate = 2 moles of ATP per glucose molecule
4
Q
What is ATP needed for?
A
Needed to maintain RBC shape, flexibilty, osmotic equilibrium and membrane integrity through cation pumps
5
Q
What does decreased ATP production cause?
A
Increased osmotic fragility
6
Q
What happens in the Hexose Monophosphate (HMP) shunt?
A
Pathway produces reduced nicotinamide adenine dinucleotide phosphate (NADPH) and reduced glutathione (GSH) necessary for maintaining hemoglobin in the reduced functional state
HMP shunt is functionally dependent on G6PD
7
Q
What happens when the HMP shunt is defective?
A
Hgb sulfhydryl groups are oxidized = Heinze bodies
Damaged RBC’s are removed by spleen
8
Q
What deficiency is a result from defective HMP shunt?
A
G6PD deficiency
9
Q
What does GSH do?
A
High concentrations present to protect RBC against oxidants by inactivating these oxidants
Oxidants are produced by macrophages during infecting or RBC in the presence of some drugs
10
Q
What is the Methemoglobin Reductase Pathway essential for?
A
Maintains heme iron in reduced state, Fe++
11
Q
What is hemoglobin in Ferric state known as?
A
Fe+++ is methemoglobin and can’t bind O2
12
Q
What 2 pathways protect heme iron from Oxidation?
A
Methemoglobin reductase and Embden-Meyerhof pathway
13
Q
What happens if the methemoglobin reductase can’t keep up with challenges by oxidant drugs?
A
High levels of methemoglobin = cyanosis due to increase concentration of deoxyhemoglobin
14
Q
What is the Rapoport-Leubering Shunt?
A
Part of Embden-Meyerhof pathway
Produces 2,3-DPG
15
Q
What is function of 2,3-DPG?
A
When hemoglobin binds 2,3-DPG O2 is released
An increase in 2,3-DPG = increase release of O2 to tissues = decreased affinity for O2
16
Q
What is Pyrvate kinase deficiency?
A
Defect in glycolytic pathway?
17
Q
What are characteristics of G-6-PD deficiency?
A
Seen during WWII, antimalarial drugs caused severe hemolysis; 10% of african americans were affected
GSH levels fall because NADPH synthesis is decreased = oxidants damage cell = denatured Hgb precipitates as Heinze bodies = Extravascular hemolysis
18
Q
What G6PD variants are associated with hemolysis?
A
GdA - Most common; 10% of African Americans
Gdmed - 2nd most common; seen in caucasions
GdB - normal genotype and present in 70% of caucasusions
19
Q
What are triggers for hemolysis?
A
Infection
Oxidant drugs therapy
Favism - severe hemolytic episode after eating fava beans (occurs in Gdmed)
20
Q
What is heme?
A
An iron-chelated porphyrin ring that functions as a non-amino acid component of a protein
Porphyrin ring is composed of a tetrapyrrole ring with Fe++ inserted in the center
21
Q
What forms of hemoglobin are found in the Embryo?
A
Gower 1
Gower 2
Portland
-not detectable after the 3rd month of gestation
22
Q
What is the primary hemoglobin in the fetus?
A
Hgb F (2 alpha + 2 gamma)
90-95% until 34-36 weeks
50-85% at birth
23
Q
What is the primary hemoglobin found in adults?
A
Hgb A
2 alpha chains + 2 beta chains)
24
Q
At what age does an infant reach adult levels of hgb A?
A
By one year
25
What is hemoglobin A2?
Normal variant of Hgb A
2 alpha chains + 2 delta chains
1% in newborn and 2-4% in Adults
26
How much Hgb F is found in normal adult?
2% - most is restricted to 8% of all RBC called F cells
| The switch from Hgb F to Hgb A is incomplete and reversible
27
What regulates hemoglobin production?
ALAS enzyme
Negative feedback of heme
Concentration of Iron
Regulation of Globin chain synthesis
28
What is the function of Hemoglobin
Transport and exchange gasses; primarily O2 and CO2
29
What is P?
Partial pressure each gas exerts into the atmostmphere
30
Why is O2 released to tissues?
oxygen is released because the PO2 (partial pressure of oxygen) in blood is more than in the tissues, and CO2 diffuses into the blood because PCO2 (partial pressure of carbon dioxide) is greater in tissues than in blood.
Gas goes from greater to less
Lungs have high partial pressure
Tissues have low partial pressure
31
What does increased O2 affinity mean?
Hemoglobin has a high affinity for O2 and does not give it up
32
What is P50?
Oxygen affinity of hemoglobin is expressed as PO2 where 50% of the Hemoglobin is saturated with O2.
Normal P50 is 26 mm HG
33
How many O2 molecules can one hemoglobin bind?
4 O2 molecules
34
What does a right shift oxygen dissociation curve cause?
```
O2 affinity is decreased - More O2 released to tissues
Increase temp
Increas 2,3 DPG
Decreased pH
Increased P50
```
35
What does a left shift oxygen dissociation curve cause?
```
O2 affinity is increases - less O2 released to tissues
Decreased temp
Decreased 2,3 DPG
Decreased P50
Increased pH
```
36
What is the difference of oxygen affinity of HgB F and HgB A?
Hgb F has a higher O2 affinity than Hgb A
| Hgb F does not readily bind to 2,3-DPG
37
What is the Bohr effect?
The effect of pH on oxygen affinity
38
What changes occur is stored blood?
pH goes down due to lactic acid from anaerobic glycolysis and K+ increase
2,3-DG decreases = decrease affinity for O2 - Hgb doesn't release)
39
What kind of hemoglobinopathy is sickle cell?
Qualitative hemoglobin disorder
40
What kind of hemoglobinopathy is thalassemia?
Quantative hemoglobin disorder
41
What are the types of qualitative globin chain abnormalities?
Substitution of a amino acid for another
Deletion of AA from the globin chain
Addition of AA to the globin chain
Globin chain fusion
42
What is hemoglobin electrophoresis?
Uses a red cell hemolysate
Two types are required because some Hb variants migrate to the same position on one type but will separate on the other type.
- Cellulose acetate: pH 8.4 – 8.6
- Citrate agar: pH 6.0 – 6.2
Interpretation: based on known migration patterns of variant Hb and comparison with controls
43
What are the normal hemoglobin electrophoresis values?
HbA (A1): 96 – 98%
HbA2: 1.5 – 4.0%
HbF: 60-90% immediately after birth
<2% after age 1
44
What are the characteristics of Hereditary Persistance of Fetal Hemoglobin?
Benign
Large amts of fetal hemoglobin in adult
Caused by suppression of beta chain synthesis so increase in gamma chains = Hgb F
45
What are the test for hemoglobin F?
- Alkali denaturation: fetal hemoglobin is more resistant to denaturation under alkaline conditions strong alkali such as NaOH or KOH used
- Kleihauer-Betke (acid elution)
- Flow Cytometry: detects intracellular HbF
46
What is the amino acid substitution for Hgb S?
ß2 6GLU→VAL
- Mutation in SIXTH position of A3 helix of the ß-chain > from POLAR glutamic acid to NON-POLAR valine (net decrease in negative charge)
- Change in electrophoretic mobility
47
What causes cells to sickle in Hgb S?
The HbS molecule undergoes gelation (crystallization) causing sickling of the red cells when the oxygen tension is reduced
HbS is less soluble than HbA
Hgb crosslinks itself
48
What does the hgb electrophoresis look like in HgB S?
80% Hgb S
Up to 20% of Hgb F
3-4% of Hgb A2
NO Hgb A because abnormal Beta chain
49
What is the half life of sickle cells?
10-20 days
50
What is amino acid substitution for Hgb C?
ß6GLU→LYS
51
What are the characteristics of hemoglobin C?
HbC tends to crystallize when dehydrated
Fragmentation may occur resulting in the production of microspherocytes which are removed in the spleen.
If the spleen is nonfunctional or has been removed, HbC crystals will be seen in the peripheral blood.
HbC disease (HbCC) results in mild to moderate anemia. Severe if sickle cell also present
52
What areas of the world are thalassemia common?
Mediterranean and Africa, through the Middle East, India, Burma, and Southeast Asia
53
What causes thalessemias?
This disorder is the result of decreased or absent production of a globin chain, a decrease in the amount of normal Hb is seen
Results in a microcytic, hypochromic anemia
54
What are the characteristics of Beta thalassemia?
Also known as Cooley’s anemia or thalassemia major
First manifests in infants with failure to thrive, pallor, moderate icterus and massive hepatosplenomegaly
Chronic hemolysis in bone marrow
Most patients present with severe anemia and need blood transfusion
Can be mild in some individuals; Most patients die in childhood if severely affected
55
What are the characteristics of beta thalassemia minor?
Heterozygous beta thalassemia
No characteristic clinical picture - may vary from a moderately severe anemia to completely asymptomatic
In severe forms, pallor and splenomegaly may be present
In nearly all cases, red cells are microcytic, hypochromic
56
Why is low oxygen a problem for SCD patients?
Hypoxemia and metabolic acidosis can trigger intravascular sickling, thus extending the clinical problem from anemia to sickle vaso-occlusion.
57
What sickle cell percentage has been shown to be less likely to have vaso-occlusion crisis?
3040% of hgb S
58
What are complications of SCD?
```
Acute vaso-occlusive pain crisis
Acute splenic sequestration crisis
Aplastic crisis
Stroke: 8-10% have at least 1 stroke
Acute chest syndrome
Acute papillary necrosis
End-stage renal disease
Priapism
Hepatic crisis
Sepsis
Skin ulcers
```
59
What is a method to detect early signs of a stroke in SCD patients?
Children with SCD who have elevated cerebral blood flow as determined by Transcranial Doppler (TCD) ultrasonography seem to be at an increased risk for developing stroke.
60
Why are SCD patients at risk for alloimmunization?
- 95% of donor pool is of European ancestry, so disparity exists between red cell phenotypes of the donors and the recipients who are of African ancestry
- SCD patients have altered immune states
- Repeated, small dose transfusions (immune system is not overwhelmed at any one time
61
What are strategies to minimize alloimmunization?
- Minimum standard practice in U.S. – red cells selected for transfusion are matched prophylactically for antigens in the Rh and Kell systems, as these are the antibody specificities most likely to form; these donor units must also be HbS negative and leukoreduced
- Phenotypically (genotypically) matched based on patient’s antigen profile
- For those patients who develop antibodies to high incidence antigens or to Rh variants: match with donors on a molecular level
62
What are the goals for transfusion in thalessmia patients?
- Correction of anemia
- Suppression of ineffective erythropoiesis
- Inhibition of the excessive gastrointestinal absorption of iron
- A “moderate transfusion” protocol is recommended, which aims to keep the pretransfusion hemoglobin between 9 to 10 g/dL; typically this consists of transfusing 10mL red cells/kg body weight every 4 weeks
63
What is the solubility of Hgb S?
Solubility of HbS in deoxygenated state is markedly reduced.
Polymerization when O2 saturation falls below 85%.
Sickling reversible with re-oxygenation.
Repeated cycles of sickling results in irreversible sickling (increase Ca+, loss of K+ and water>increase Hg concentration.
Irreversibly sickled cells due to damage to submembrane skeletal lattice > brittle.
Decreased oxygen affinity causes a right shift in oxygen dissociation curve.
64
What disease does SC trait protect from?
Plasmodium falciparum
65
How common is sickle cell?
SCT: 1 out of every 12 African American births
SCD: 1 out of every 500 African American births
66
What is vaso-occulsion crisis?
O2 dissociates to surrounding tissue resulting in hypoxic environment > More cells sickle and cause blockage of microvasculature
Can cause local tissue necrosis
Occurs in tissues prone to vascular stasis (spleen, marrow, retina, kidney)
67
What is the result of splenic atrophy in SCD patients?
```
Lung infections
- Streptococcus pneumoniae
- Haemophilus influenzae
Acute Chest Syndrome
Osteomyelitis
- Salmonella sp.
- Staphylococcus aureus
- Gram-negative enteric bacilli
Aplastic Crisis -Cessation of erythropoiesis
Viral or bacterial infections
Mycoplasma infections
Cardiac overload from attempt to compensate for anemia due to acute hemolysis.
```
68
Why is hydroxyurea given to sickle cell pateints?
Increases Hgb F
May reduce hospitalizations and acute chest syndrome
variable response due to haplotype and differing HbF percentages
Side effect: myelotoxic
69
What are the common difference in phenotype between Caucasians and blacks?
68% of W and 27% of B are C+
66% of W and 10% of B are Fya+
74% of W and 49% of B are Jkb+
51% of W and 31% of B are S+
70
What is most common Rh phenotype in the black population?
Ror - Dce
Found in <2% of white donors
Can use Rh neg units (rr)
71
How do transfuse when Rh varaints are present?
Partial RH variants > RH negative units
| Weak RH variants > RH positive units
72
What is the frequency of Rh variants in the black population?
7% have partial D
30% have partial C
2% have partial e
73
What are the common immunologic D variants?
DAR
DIIIa
DAU (RH32) encoded by RN haplotype
DAK encoded by DIIIa, DOL and RN haplotypes
74
What are the common immunologic C variants?
```
VS antigen (RH20, Encoded by RHCE*ceS allele)
32% of African American pts VS positive
0.01% of White donors VS positive
```
75
What low incidence antigens are more common in African Americans?
Js(a) antigen
20% of African American recipients
0.01% of white donors
76
What hign incidence antigens are more common to be negative in African Americans?
U and Js(b) negative are more common in Blacks
77
Why are autoantibodies common in SCD?
Chronic inflammatory state
Elevated CRP and cytokines (IL-1, IL-6, IFNγ)
CD4+ regulatory T lymphocyte (Tregs) suppression
6-10% of SCD patients develop autoantibodies after alloimmunization
Causes hyperhemolysis during DHTRs
78
What causes DHTR in SCD patients?
~30% of DHTRs attributable to IgG autoantibodies with C3-mediated hemolysis
70% from preformed antibodies at undetectable levels (-Fya, -Jkb, -S)
79
What is normal MCV?
80-100
Microcytic is less than 80
Macrocytic is greater than 100
80
What are some examples of microcytic anemia
```
Anemia of Chronic Disease
Thalassemias
Sideroblastic
Myelodysplastic Syndrome
Refractory Anemia with Ringed Sideroblasts (RARS)
```
81
What conditions cause anemia of chronic disease?
```
Second most common anemia
Chronic infections
Chronic inflammation
Trauma
Organ failure
Malignancies
```
82
What is the mechanism of anemia of chronic disease?
Cytokines inhibit release of iron from stores
IL-6 produces hepicidin
Serum ferritin is increased - acute phase reactant
83
What is the function of hepicidin?
Beneficial in microbial infections
Sequestration of iron in macrophage & liver cells
Decreases iron absorption from the gut
Suppression of erythropoietin production
84
What causes beta thalassemia?
Reduced Beta chain production
Excess Alpha chains precipitate in cell
Reduced Hgb A and Increased Hgb F
85
What are some examples of sideroblastic anemia?
Myelodysplastic Syndrome such as; RARS: refractory anemia with ringed sideroblasts
Or Secondary due to malignancy, drugs, lead, and alcohol
86
What are the characteristics of siderblastic anemia?
```
Moderate to severe anemia
Elevated RDW
Microcytes and normocytes
Papenheimer bodies (prussian blue)
TIBC Normal – Low
Iron saturation Very high (100%)
Serum ferritin High
```
87
What are some examples of macrocytic anemia?
```
Non-Megaloblastic
- Chronic Liver Disease
Megaloblastic
- Vitamin B12 Deficiency
- Folic Acid Deficiency
- Malignancy
```
88
What is the mechanism of megaloblastic macrocytosis?
```
Impaired DNA synthesis
Asynchronous maturation
- Cytoplasm matures at a normal rate
- Nucleus matures slowly
- Cytoplasm continues to develop
- Cell continue to grow
```
89
What are drugs that cause megaloblastic microcytosis?
```
Chemotherapeutic drugs
- purine antagonists
- pyrimidine antagonists
Antibiotics
Folate antagonists
- Anti-retrovirals (AZT)
Hydroxyurea - Used to treat vaso-occlusive pain crisis in sickle cell disease
```
90
How does alcoholism cause macrocytic anemia?
Can be either megaloblastic or non-megaloblastic or both
Chronic liver disease (normoblastic)
Nutritional deficiency (megaloblastic)
- Vitamin B12
- Folic Acid
Direct bone marrow toxicity (normoblastic)
most common
91
What are causes of B12 deficiency?
```
Diet - Vegan or Alcoholic
HIV Infections
H. pylori Tape worms
Pernicious anemia - NO Intrinsic factor
Absorption issues- Crohn’s disease, Celiac disease, Grave’s disease, Ileal/gastric resection
Drugs
```
92
What are causes of Folate deficiency?
```
Usually in the elderly
alcoholics
Increased requirement due to elevated cell proliferation
Hemolytic anemias
Myeloproliferative diseases
Cancer
Pregnancy
```
93
What is pancytopenia?
Hct <20% with marked reticulocytopenia
Granulocyte count <500/μL
Platelet count <20,000/μL
Markedly hypocellular marrow with <20% hematopoietic cells for >3 weeks
94
What are causes of pancytopenia?
```
Marrow Failure Syndrome
- Hypoproliferative and aplastic anemias
- Bone marrow replacement
Ineffective Hematopoiesis
- Megaloblastic anemias or MDS
Hemodilution
Hypersplenism/Splenomegaly
Immune Destruction (Autoimmune disease
```
95
What causes aplastic anemia?
Some association with drug exposure
Chloramphenicol and phenylbutazone among others
Hepatitis B, CMV, EBV and parvo B-19
Viral agents infect the bone marrow stem cells.
Exposure to other toxins: chemical solvents (ex. Benzene), irradiation or cytotoxic drugs
96
What are treatment options for Fanconi's Anemia?
Transfusion to support
BMT
Gene therapy
97
What is Fanconi's anemia
Inherited aplastic anemia
Chromosomes break apart and rearrange easily
Leads to bone marrow failure
98
What is polycythemia vera?
Myeloproliferative cell disorder
Unregulated growth and proliferation of hematopoietic precursors with excessive erythrocyte proliferation.
Clonal proliferation – single cell is the source of the proliferation.
Unregulated division of this cell leads to many daughter cells that in turn proliferate.
Since involves multipotent stem cell, other cell lines can also be affected
99
What is clinical presentation of Polycythemia vera?
```
Ruddy complexion
Cherubic faces
Symptoms of hyperviscosity due to too many RBCs in circulation, making blood viscous
Headaches
Visual disturbances
Thrombotic events
```
100
What is hereditary hemochromatosis?
Hemochromatosis is a clinical disorder that results in parenchymal tissue damage due to the iron overload.
Excess deposits of iron are store in macrophages, hepatocytes, cardiac cells, endocrine cells and other tissue.
The results is that iron interferes with the normal function of the cells or may even cause cell death.
101
What causes hereditay hemochromatosis?
Mutation in the HFE gene produces an abnormal protein that binds to the transferrin receptors on cells
Results in a 5 to 10-fold decrease in the affinity between transferrin and its receptor.
Excess iron is absorbed from the GI tract and cannot be excreted, resulting in iron deposition in the liver (0.5 – 1.0 gm/yr)
102
What is hematologic hypoplasia?
Decrease in hematopoietic cellularity
Depletion, damage, inhibition of HPCs
Hematopoietic tissue replaced by fat
Lineage-specific cytopenia or pancytopenic
103
What conditions are spherocytes seen in?
```
Hereditary spherocytosis
Accelerated rbc destruction by reticuloendothelial system
Some hemolytic anemias
Severe burns
Transfused cells
MCHC is high
```
104
What conditions are leptocytes seen in?
```
AKA “target cells” or codocytes
May be bell-shaped
Thalassemias
Obstructive jaundice
Hemoglobinopathies
Splenectomy
Iron deficiency anemia
```
105
What conditions are stomatocytes seen in?
```
Hereditary defect in membrane transport of sodium
Severe liver disease
Alcoholism
Rh null phenotype
Artifact
```
106
What conditions are elliptocytes seen in?
Hereditary elliptocytosis
Thalassemia major
Iron deficiency anemia
Myelophthisic anemias
107
What conditions are schistocytes seen in?
```
Increased intravascular mechanical trauma
Microangiopathic hemolysis
Hemolytic anemias
Hemolytic uremic syndrome
TTP
Renal graft rejection
```
108
What conditions are acantocytes seen in?
```
Irreversibly abnormal membrane lipid content
Liver disease
Abetalipoproteinemia
Hypothyroidism
Vitamin E deficiency
Splenectomy
Malabsorption
```
109
What conditions are echinocytes seen in?
Reversible abnormality of the membrane lipids
High plasma-free fatty acids
Bile acid abnormalities
Effects of drugs (barbiturates, salicylates)
Microangiopathic hemolytic anemia
Pryuvate kinase deficiency
Uremia
110
What conditions are dacryocytes seen in?
Myelofibrosis with myeloid metaplasia
Thalassemias
Myelophthisic anemias
Extramedullary hematopoiesis
111
What condition are depranocytes seen in?
Sickle cells
Repeated sickling events damage the surface membrane, the cell remains sickled even when reoxygenated – becoming irreversibly sickled cells.
112
What are the characteristics of Hereditary Sperocytosis?
Defective spectrin or attachment of spectrin to lipid bilayer
Increase permeability to NA, must use ATP to pump out > trapped in splenic cords with no ATP = hemolysis
Mild-mod anemia; compensated except during crisis
113
What are the characteristics of Hereditary Elliptocytosis?
46 mutations in genes encoding a-spectrin,
b-spectrin, protein 4.1
Usually asymptomatic; usually compensated
Extravascular hemolysis in spleen
Africa & Mediterranean Regions associated with the prevalence of malaria
114
What are the characteristics of SE asia ovalocytes?
Autosomal dominant: all patients are heterozygotes
Common in malaria belt - As high as 30% of population
Single 27 base pair deletion mutation in the gene encoding Band 3
Strengthens the bond between Band 3 and ankryn
Increased membrane rigidity; sensitive to osmotic changes
Resistance to Plasmodium falciparum
No treatment
115
What are the characteristics of hereditary stomatocytosis?
Defects in membrane cation transport protein
Normally K+ pumped in and Na+ pumped out
Defect results in inability to efficiently pump ions
Increased osmotic fragility
116
What is Xerocytosis?
Dehydrated hereditary stomatocytosis (DHS)
| Excessive permeability to potassium results in loss of water and dehydration of the cells
117
What is hydrocytosis?
Hydrocytosis: Overhydrated
Increased intracellular sodium and decreased potassium
Rh null syndrome: RhAG-associated stomatocytosis
118
What is acquired Paroxysmal Nocturnal Hematuria (PNH)?
Group of acquired mutations in clonal hemopoietic stem cells resulting in defective GPI-anchored, complement-inhibiting proteins Decay Accelerating Factor (DAF, CD55) and protectin (CD59)
Complement mediated hemolysis = severe anemia
119
What are characteristics of TTP?
MAHA seen more common Young Adult Females
Deficiency of ADAMST-13 a Von Willebrand Factor Cleaving Protease
ADAMST-13 prevents clotting in microvasculature
Idiopathic, hereditary, secondary
Idiopathic = autoimmune (anti-ADAMST-13 antibodies)
Pregnancy, Oral contraceptives, Lupus, Drug Allergies
Treatment - plasmapheresis
120
What are the most common causes of HUS?
Shiga toxin associated (stx-HUS)
| Shiga toxin producing E. coli
121
What is a clinical feature of HUS?
```
Evidence of renal failure
Elevated serum creatinine
Proteinurea
Hematuria
Hyaline, granular and RBC casts in urine
```
122
What are characteristics of HELLP
Abnormalities in development of placental vasculature
Platelet activation & fibrin deposition in maternal microvasculature
Primarily affects liver
Symptoms: Dangerously high blood pressure, Proteinuria, and Fluid retention
123
What infectious agents cause RBC hemolysis
Malaria
babesiosis
Clostridium perfringens
Bartonella bacilliformis
