Practical Clinical Hematology. 4. Sickle Cell. What is Sickle cell:. Sickle cell anemia is an inherited disorder that leads to the production of an abnormal hemoglobin variant, hemoglobin S (HbS)
Practical Clinical Hematology
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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
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 10-20 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.
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
A saline citrate with paraffin oil.
Sodium Metabisulfite Method.
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
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
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 .
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.
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.