Transcript Sickle cell test

Sickle Cell Anemia
Prepared by:
Ibtisam H. Al Aswad
Reham S. Hammad
INTRODUCTION
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Sickle Cell Anemia is a
hereditary disease which is
cause by a disorder in the
blood, a mutation in the
Hemoglobin Beta Gene
which can be found in the
chromosome 11.
This disease causes the
body to make abnormally
shapes red blood cells.
A normal red blood cell is
shaped as a round donut
while the abnormal red
blood cell has a “ C “ form.
INTRODUCTION
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Hemoglobin molecules in each red
blood cell carry oxygen from the lungs
to body organs and tissues and bring
carbon dioxide back to the lungs .
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In sickle cell anemia, the hemoglobin
is defective. After hemoglobin
molecules give up their oxygen, some
may cluster together and form long,
rod-like structures. These structures
cause red blood cells to become stiff
and assume a sickle shape.
Characters of Sickled Red Cell
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Changing the shape of the RBC from a round
disc to a characteristic crescent (sickle) shape.
Sickled red cells cannot squeeze through small
blood vessels .
They stack up and cause blockages that deprive
organs and tissues of oxygen-carrying blood .
This process produces periodic episodes of pain
and ultimately can damage tissues and vital
organs and lead to other serious medical
problems .
Characters of Sickled Red Cell
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Normal red blood cells live about 120 days in the
bloodstream, but sickled red cells die after about
10 to 20 days .
Because they cannot be replaced fast enough,
the blood is chronically short of red blood cells, a
condition called anemia.
Inheritance
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Sickle cell anemia is an autosomal recessive
genetic disorder caused by a defect in the HBB
gene, which codes for hemoglobin.
The presence of two defective genes (SS) is
needed for sickle cell anemia.
Hemoglobin S differs from normal adult
hemoglobin (hemoglobin A) only by a single amino
acid substitution (a valine replacing a glutamine in
the 6th position of the beta chain of globing).
When a person has two copies of the S gene
(homozygous SS), he has sickle cell anemia.
Inheritance
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In sickle cell disease, as much as 80% to 100% of
the hemoglobin may be HbS.
A person with one altered S gene will have sickle
cell trait.
In those who have sickle cell trait, 20% to 40% of
the hemoglobin is HbS.
The person does not generally have any symptoms
or health problems but can pass the gene on to his
children.
Inheritance
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If each parent carries one sickle hemoglobin
gene (S) and one normal gene (A), each
child has a 25% chance of inheriting two
defective genes and having sickle cell
anemia.
25% chance of inheriting two normal genes
and not having the disease.
50% chance of being an unaffected carrier
like the parents.
Pathophysiology
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Normal hemoglobin exists as
solitary units whether
oxygenated or deoxygenated
(upper panel). In contrast,
sickle hemoglobin molecules
adhere when they are
deoxygenated, forming sickle
hemoglobin polymers ( lower
panel).
Pathophysiology
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Normal red cells maintain their
shape as they pass through the
capillaries and release oxygen to
the peripheral tissues (upper
panel). Hemoglobin polymers
form in the sickle red cells with
oxygen release, causing them to
deform. The deformed cells
block the flow of cells and
interrupt the delivery of oxygen
to the tissues (lower panel).
Pathophysiology
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Hemoglobin S production arises from an altered
(mutated) “S” gene.
Hemoglobin S differs from normal adult
hemoglobin (hemoglobin A) only by a single amino
acid substitution (a valine replacing a glutamine in
the 6th position of the beta chain of globing).
Sickle cell test
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A sickle cell test is a blood test done to screen for
sickle cell trait or sickle cell disease. Sickle cell
disease is an inherited blood disease that causes
red blood cells to be deformed (sickle-shaped).
If the screening test is negative, it means that the
gene for sickle cell trait is not present.
If the screening test is positive, then further
haemoglobin testing must be performed to confirm
whether one mutated gene or both are present. In
unaffected individuals HbS is not present
Sickle cell test
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Principle:
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When a drop of blood is sealed between a cover
slip and a slide, the decline in oxygen tension
due to oxidative processes in the blood cells
leads to sickling.
When we add a chemical reducing agents,
Sodium dithionite or sodium metabisulfite. This
rapidly reduces oxyhemoglobin to reduced
hemoglobin, and this property suggested its use
in testing erythrocytes for sickling.
1-Sodium Metabisulfite Method
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Specimen:
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Whole blood using heparin or EDTA.
Reagent and equipment:
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Sodium Metabisulfite 2% (w/v ).
Petroleum jelly.
Cover glass.
Microscope.
Procedure
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Place one drop of the blood to be tested in a glass
slide.
Add 1- 2 drops of sodium metabisulfite to the drop of
blood and mix well with an applicator stick.
Place a cover glass on top of the sample and press
down lightly on it to remove any air bubbles and to
form a thin layer of the mixture. Wipe of the excess
sample.
Carefully rim the cover gloss with the petroleum jelly,
completely sealing the mixture under the cover slip.
Examine the preparation for the present of sickle cells
after one hour using 40 X objective.
2-Solubility test
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Principle:
 Erythrocytes
are lysed by saponin.
 The released hemoglobin is reduced by
sodium hydrosulfite in a concentrated
phosphate buffer.
Sickle cell test
 Under these conditions, reduced HbS is
characterized by its very low solubility and the
formation of crystals.
 The presences of HbS or HbC are indicated
by the turbid solutions.
 The normal HbA under these same conditions
results in a clear non-turbid solutions.