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Hematology Unit 1 > Sickle Cell Disease (complete) > Flashcards

Sickle Cell Disease (complete) Flashcards

1
Q

Explain the molecular bases for sickle cell disease.

A
  • Both Beta-globin genes are mutated
  • At least one w/ Beta6 glu –> val and the other abnormal in the same or different way
  • Called sickle disease w/ two glu–> val
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2
Q

What is the mode of inheritance of sickle cell disease?

A

Autosomal recessive

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3
Q

How does the sickle cell mutation lead to the phenotype?

A
  • HbSS are easily lysed
  • Don’t last long
  • Normal looking w/ O2
  • When O2 is released, create the sickle shape — cells clump together
  • Can only last a few cycles (fewer than normal)
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4
Q

Describe the geographic distribution of sickle cell disease

A
  • Most common in African, Indian, Middle Eastern, and Mediterranean pop’n
  • Think: around equator
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5
Q

Describe a situation where people heterozygous for sickle cell disease may have a survival advantage.

A

Reduced risk of morbidity and mortality of malaria

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6
Q

Describe findings on CBC for pts w/ sickle cell disease

A

RI: increased
WBC: increased
Platelets: increased
RDW: increased

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7
Q

What are other abnormal chemistry findings in pts w/ sickle cell disease? Why?

A

Total/indirect bilirubin: increased
LDH: increased
AST: increased

All released from lysed RBCs

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8
Q

Describe findings on peripheral blood smear for pts w/ sickle cell disease

A
  • Sickle forms
  • Schistocytes
  • Polychromasia
  • Anisocytosis
  • Poikilocytosis
  • Howell-Jolly bodies
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9
Q

What are schistocytes?

A

“Broken” irregular cells

http://en.wikipedia.org/wiki/Schistocyte

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10
Q

What is polychromasia?

A
  • Blue-colored cells
  • Represent reticulocytes

http://en.wikipedia.org/wiki/Polychromasia

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11
Q

What is anisocytosis?

A

Variation in RBC size

http://en.wikipedia.org/wiki/Anisocytosis

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12
Q

What is poikilocytosis?

A

Variation in RBC shape

http://en.wikipedia.org/wiki/Poikilocytosis

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13
Q

What are Howell-Jolly bodies?

A

Small purple dots w/in RBCs

Seen in pts w/o a functional spleen

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14
Q

What is sickle trait?

A

Occurs in a person w/ 1 sickle gene and 1 NORMAL gene

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15
Q

What are the consequences of sickle trait?

A
  • Normal gene produces Beta-globin chains in normal quantities
  • This protects against development of sickle cell disease
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16
Q

What are the major variants of sickle cell disease?

A

1) Sickle Cell Anemia
2) Sickle B(0) thalassemia
3) Sickle- Hb C
4) Sickle B(+) thalassemia
5) Sickle Cell Trait

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17
Q

Describe sickle cell anemia. Include Beta-globin gene types, normal Hb amount, normal retic count, size of RBC, clinical severity.

A

B-globin genes: S+S

Hb count: 6-9 (nl: 14=16g/dl)

Retic count: 5-30% (nl: 1-2%)

RBC size: Normal

Clinical Severity: 4+ (worst)

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18
Q

Describe Sickle B(0) Thalassemia. Include Beta-globin gene types, normal Hb amount, normal retic count, size of RBC, clinical severity.

A

B-globin genes: S+B(0)

Hb count: 6-9 (nl: 14=16g/dl)

Retic count: 5-30% (nl: 1-2%)

RBC size: Small

Clinical Severity: 4+ (worst)

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19
Q

Describe Sickle Hb C. Include Beta-globin gene types, normal Hb amount, normal retic count, size of RBC, clinical severity.

A

B-globin genes: S+C

Hb count: 10-12 (nl: 14=16g/dl)

Retic count: 3-5% (nl: 1-2%)

RBC size: Normal

Clinical Severity: 2+ (mid)

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20
Q

Describe Sickle B(+) Thalassemia. Include Beta-globin gene types, normal Hb amount, normal retic count, size of RBC, clinical severity.

A

B-globin genes: S+B(+)

Hb count: 11-13 (nl: 14=16g/dl)

Retic count: 3-5% (nl: 1-2%)

RBC size: Small

Clinical Severity: 2+ (mid)

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21
Q

Describe Sickle Cell Trait. Include Beta-globin gene types, normal Hb amount, normal retic count, size of RBC, clinical severity.

A

B-globin genes: normal+S

Hb count: 14-16 (nl: 14=16g/dl)

Retic count: 1-2% (nl: 1-2%)

RBC size: Normal

Clinical Severity: 0 (not severe)

22
Q

Describe the deoxygenated state of HbS

A

HbS polymerizes into 14-strand helical fibers

These distort shape — membrane is damaged

23
Q

Describe the reoxygenated state of HbS

A
  • Polymers dissolved

- Normal shape achieved

24
Q

What happens to HbS after several deoxy-reoxy cycles?

A
  • Cell becomes irreversibly sickled

- Then lysed/destroyed

25
Q

What happens to HbS shape in presence of other Hb?

A
  • Normal Hb or HbC interfere w/ polymerization process
  • Lessens tendency for RBC sickling/membrane injury
  • Lessens disease
26
Q

What are the signs and symptoms of sickle cell disease?

A

1) Chronic hemolytic anemia
2) Chronic RBC adhesion/vascular occlusion
3) Acute RBC adhesion/occlusion

27
Q

Describe chronic hemolytic anemia as it relates to sickle cell disease

A
  • Sickle RBC is fragile/rigid —> chronic RBC destruction

- Sickle RBCs only last 20 days —> ^RI, ^WBC, ^platelets, ^RDW

28
Q

Describe chronic RBC adhesion/vascular occlusion as it relates to sickle cell disease

A
  • RBCs extra sticky b/c of membrane injury/retention of adhesion molecules at cell surface
  • Cell adhesion —> vaso-occlusion, vessel wall injury, endothelial remodeling —> vessels narrow —> chronic organ damage
29
Q

Which organs are chronically damaged due to chronic RBC adhesion in sickle cell disease?

A

1) Spleen
2) CNS
3) Lungs
4) Kidney
5) Retina
6) Femoral/humeral heads
7) Skin

30
Q

Describe the chronic damage on the spleen in sickle cell disease

A
  • Large # of RBCs trapped —> splenic sequestration, chronic circulation occlusion
  • Causes tissue death (autoinfarction)
  • Compromises spleen’s killing of bacteria
31
Q

Describe the chronic damage on the CNS in sickle cell disease

A
  • Large blood vessels damaged by sickle RBCs
  • 10% of kids w/ HbSS have stroke
  • Adults more likely to have hemorrhages from progressive vessel weakening —> rupture
32
Q

Describe the chronic damage on the lungs in sickle cell disease

A

Damage to vessel in lungs —> ^ pressure in pulm arteries

Causes strain of R side of heart (30-40% of pts)

Most common cause of death for sickle cell disease

33
Q

Describe the chronic damage on the kidney in sickle cell disease

A

Tubules damaged by chronic vaso-occlusion —> inability to concentrate urine

Leads to dehydration, blood in urine, glomeruli enlargement, protein in urine

In 10% of pts

34
Q

Describe the chronic damage on the retina in sickle cell disease

A

Retinal vessel damage —> retinal detachment/blindness

35
Q

Describe the chronic damage on the femoral/humeral heads in sickle cell disease

A

Avascular necrosis —> chronic pain/joint deterioration

Can require joint replacement surgeries

36
Q

Describe the chronic damage on the skin in sickle cell disease

A

Can cause ulcers, often on ankles

Microvascular ischemia and poor healing

37
Q

Describe acute RBC adhesion/occlusion

A

AKA: sickle cell crisis

hypoxia, dehydration, inflammation, infection —> sickle RBCs damaged —> sudden vaso-occlusion

Leads to pain crisis (b/c of reversible ischemia)

Resolves when cause resolves

38
Q

What does RBC adhesion/occlusion cause?

A

1) Splenic sequestration
2) Hand-foot syndrome
3) Acute chest syndrome
4) Acute multi-organ failure
5) Priapism
6) Bone infarction

39
Q

Describe acute chest syndrome in pts w/ sickle cell disease

A

Sickle RBCs trapped in lung circulation

Damages vessels —> fluid leaks out —> cannot oxygenate blood

40
Q

What is priapism?

A

Sickle RBCs trapped in penis, painful sustained erections

41
Q

Explain the relationship between aplastic crisis and parvovirus B19

A

Parvovirus B19 causes aplastic crisis —> fifth disease

Infection is usually quick — pts may need a transfusion

42
Q

What are the consequences of fifth disease?

A

Infects RBC precursors —> arresting their development

43
Q

What are some therapies used to treat pts w/ sickle cell disease?

A

1) Folic acid
2) Penicillin
3) Bone marrow transplantation
4) Hydroxyurea therapy
5) Transfusion therapy

44
Q

Why is folic acid used as a treatment for pts w/ sickle cell disease?

A

In response to developmental delays caused by anemia

45
Q

Why is penicillin used as a treatment for pts w/ sickle cell disease?

A

Sepsis! used as prophylactic

Splenic death can kill kids w/ HbSS

46
Q

Why is bone marrow transplantation used as a treatment for pts w/ sickle cell disease?

A

Leads to >90% disease-free survival

Only 20% of eligible pts have a donor (matched full sibling w/o HbSS)

47
Q

Why is hydroxyurea therapy used as a treatment for pts w/ sickle cell disease?

A
  • An oral chemotherapy agent —> induces production of HbF
  • HbF interferes w/ HbS polymerization
  • Improves anemia
  • Reduces acute pain crises
  • Reduces mortality
48
Q

Why is transfusion therapy used as a treatment for pts w/ sickle cell disease?

A
  • Most people don’t require these
  • Used if anemia is worsening
  • May reverse process

Can lead to iron overload

49
Q

Describe iron chelation therapy

A

Binds excess iron

Used for pts who receive multiple transfusions

50
Q

Why is iron chelation challenging for some pts?

A
  • Most common agent (deferoxamine) is infused sq in abdomen

- Requires 8-12 hrs, 5-7 times/week

51
Q

Explain how newborn screens can be used to diagnose sickle cell disease

A
  • All infants born in US are screened for hemoglobinopathies
  • Uses heel stick
  • Parental ed and prophylactic penicillin can be used ASAP to prevent early deadness

Hematology Unit 1 (12 decks)

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