cell anemia is a genetic disorder. In this disease the shape of hemoglobin
changes to sickle shape. The oxygen binding capacity of hemoglobin gets
reduced. So it is very important to predict the presence of sickle cell gene
through prenatal testing. Learn more about prenatal testing of sickle cell
cell anemia is caused by the presence of hemoglobin S in the blood stream.
There are certain specific objectives behind the prenatal testing for sickle
cell anemia, which are as follows.
- The presence of hemoglobin S is identified.
- The red blood cell count in relation to the hemoglobin
level is evaluated.
- It is checked whether the individual carries
one or more than one hemoglobin gene copy that is altered in character.
- It is also checked whether any other variant of
abnormal hemoglobin is present. But some additional tests are required to
determine and specifically identify them.
screening for sickle cell anemia
is a complicated one. The hemoglobin variants are over nine hundred in number.
So the screening must be precise enough to correctly confirm whether hemoglobin
S is at all present and the count of it. Given below are the screening
procedures that together constitute the prenatal testing for sickle cell
sickle cell anemia is a genetic disease, the direct members of the family tree
of the individual who already has sickle cell traits are screened. Even people
who are not screened at birth or those who are unaware of the results of the
screening that were performed on them when they were a child can opt for this
screening. There are two tests that are performed:
S Solubility Test and Sodium Metabisulfite Test
These are combination tests that screen for presence
of hemoglobin S. a blood sample is obtained from the individual and some
chemicals are added to it to reduce the oxygen level of the sample. If the
individual happens to have a sickle cell trait, which means even a single
sickle cell gene, hemoglobin S is sure to be present. Since the oxygen levels
are reduced, the abnormal sickle cells will be formed.
The final screening, confirmation and diagnosis are
done through the following tests:
(Hb) Evaluation – The normal and abnormal hemoglobin types are
varied and many in number. So the relative amounts of each of them are
evaluated through a series of tests. The Hb evaluation method can specifically
identify the particular variant of hemoglobin so that the identification and
quantification becomes easier. The evaluation involves the following methods:
Hemoglobin Electrophoresis – This is a
traditional common method that identifies the presence of various hemoglobin
Hemoglobin Fractionation – This is a
popular method that screens hemoglobin types and particularly screens for Hb S.
Isoelectric Focusing – This is a
very sensitive method that is practiced to obtain similar results as the above
testing for sickle cell currently makes the use of the Hb isoelectric
focusing in most of the countries.
DNA Analysis – This is a
very effective evaluation process as it can correctly examine and scrutinise
the alterations and mutations taking place in the genes that are responsible
for the production of the varied hemoglobin components. The test can specify
whether the individual ahs one or more than one copy of the Hb S mutation. This
therefore gives a very precise result regarding sickle cell.
Prenatal testing for sickle cell can also be
done by testing the amniotic fluid when the fetus is 14-16 week old. There are
certain risks involved I this testing procedure and it is strongly advised that
the individual and the couple go for genetic counseling before deciding on the
genetic testing. This will help them make an informed decision as the possible
outcomes of the testing will be clearly explained to them before hand.