Transcript Sickle Cell Test

Practical
Clinical Hematology
What is Sickle cell:
 Sickle cell anemia is an inherited disorder that leads to
the production of an abnormal hemoglobin variant,
hemoglobin S (HbS)
 Hemoglobin S production arises from an altered
(mutated) “S” gene. Differ on Hb A by one amino acid
substitution. .
Amino acid substitution in HbS
One S gene
SS gene (homozygous SS)
Sickle cell trait, 20% to 40% of the
hemoglobin is HbS
Sickle cell anemia, 80% to 100% of the
hemoglobin is HbS
Does not have any health problems
No symptoms under 'normal' conditions.
But in 'sickling crises' such as infection
or dehydration
There is some symptom like haemolytic
anaemia (jaundice)
RBCs have Hbs
 In the RBC, variant Hbs can form polymers in low
oxygen conditions, changing the shape of the RBC
from a round disc to a characteristic crescent (sickle)
shape.
 This altered shape limits the RBC’s ability to flow
smoothly throughout the body, limits the
hemoglobin’s ability to transport oxygen, and
decreases the RBCs lifespan from 120 days to about 1020 days.
 The affected person can become anemic because the
body cannot produce RBCs as fast as they are
destroyed.
 Also, sickled blood cells can become trapped in blood
vessels reducing or blocking blood flow. This can
damage organs, muscles, and bones and may lead to
life-threatening conditions.
Hydroxyurea as a treatment
 HbF, also called fetal hemoglobin, is the form of hemoglobin
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present in the fetus and small infants.
Most HbF disappears early in childhood, although some HbF
may persist. Fetal hemoglobin is able to block the sickling action
of red blood cells.
Because of this, infants with sickle cell disease do not develop
symptoms of the illness until. HbF levels have dropped.
Adults who have sickle cell disease but still retain high levels of
hemoglobin F generally have mild disease.
Hydroxyurea (Droxia) is a drug that reduces the severity of sickle
cell disease by stimulating production of HbF. It is currently the
only drug in general use to prevent acute sickle cell crises
Sickle cell test:
 A sickle cell test is a blood test done to screen for sickle
cell trait or sickle cell disease.
 There are three method
1. A saline citrate with paraffin oil.
2. Sodium Metabisulfite Method.
3. Solubility Test.
General Principle
 We will make the conditions at which oxygen tension
decline to induced the sickling process of Hbs in RBCs.
A saline citrate with paraffin oil
 Principle:
 a saline citrate suspension of blood is allowed to stand
in a test tube under a layer of paraffin oil until sickling
takes place.’
 In employing any of the common diagnostic tests for
sickling it is desirable to obtain blood which has a low.
fraction of oxyhemoglobin.
Sodium Metabisulfite Method
 Principle
 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.
 In this method added with blood drop a
chemical reducing agents. Such as sodium
metabisulfite.
This
rapidly
reduces
oxyhemoglobin to reduced hemoglobin, then
this will be accelerate sickling .
Solubility test
 Principle
 Erythrocytes are lysed by saponin and the released
hemoglobin is reduced by sodium hydrosulfite in a
concentrated phosphate buffer.
 Under these conditions, reduced HbS is characterized
by its very low solubility and the formation of crystals.
Principle
 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.
Discussion
 The sickle cells or the holly-leaf form of the cell must come to a point
or points to be considered positive. Elongated cells with a round end
must not be confused with sickle cells.
 Sickling of the cells is maximum at 37oC and decreased as the
temperature lowers.
 This test should not be performed on infants less than six months old.
 With this method it is not possible to distinguish sickle cell trait from
sickle cell disease. Hence if the test is positive, it is advisable to perform
hemoglobin electrophoresis to determine the presence of the trait or
the anemia and to positively identified the type of the sickling
hemoglobin present.