Blood typing and blood transfusion
Introduction:
Blood is a liquid connective tissue that consists of cells and cell fragments (named
formed elements) surrounded by a liquid extracellular matrix (or blood plasma).
Blood has three general functions: - transport,
- homeostasis,
and - protection.
Blood plasma:
- Yellowish liquid, which makes up about 55% of total blood volume
- contains approx. - 91.5% water
and - 8.5% solutes most of which are proteins like
albumins, globulins or fibrinogen
Formed elements include three principal components:
- Red blood cells (RBCs or erythrocytes; 4.8-5.4 million/μl blood),
- White blood cells (WBCs or leukocytes; 5000-10000/μl blood) and
- Platelets (thrombocytes; 150.000-400.000/μl blood).
RBCs and WBCs are whole cells, platelets are only cell fragments
Blood as a liquid connective
tissue
Blood groups and blood types
- The surface of the RBCs contains a genetically determined assortment of
antigens composed of glycoproteins and glycolipids.
- The presence or absence of these antigens or agglutinogens determines blood
group.
- The 2 most important blood grouping systems are:
1- ABO Blood group system
2. Rh blood group system
1- ABO Blood group system
- The ABO blood group is characterized by two glycolipid antigens, called A and B
depending on whether the RBCs have none, only one or both antigens
- Blood groups are distinguished as type A, B, AB or O.
- Blood plasma contains antibodies or agglutinins that react with non-self
antigens.
2- Rh blood group system
- The Rh blood group is named after the presence of the Rh factor or D antigen on
the surface of RBCs.
- People - having the D antigen are called Rh+ (Rh positive), while those
- lacking Rh antigens are regarded as Rh- (or Rh negative).
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Blood transfusion and blood groups compatibilities
- During blood transfusion, the donor RBCs should not carry antibodies against the
recipient’s blood group antigens. For example, a recipient with type A blood
should not receive blood form a donor with type B, as the latter has anti-A
(antibodies) which results in agglutination, but he/she can receive from one with
type O blood, as no antibodies will be produced against it, as O blood group
contains no antigen (as shown in figure 3).
- Agglutination is an antigen-antibody response in which foreign RBCs are cross-
linked to each other, leading to the haemolysis of RBCs and kidney malfunction.
- Accordingly, type O blood group can provide RBCs to any other ABO blood type
as no antibodies will produce against it, while type AB people can receive blood
from any other blood group as they do not have any antibodies against RBCs in
their blood plasma (Figure 3).
Regarding Rh blood group,
Normally, blood plasma does not contain anti-D antibody, however, in case an
(Rh-) person receives Rh+ blood, immunization occurs and anti-D antibodies are
produced. (See table 1)
- If a second transfusion of Rh+ blood takes place, the already formed anti-D
antibodies lead to the agglutination of the donor Rh+ RBCs.
Blood group
Donor
Rh+
Rh-
Rh+
OK
OK
Rh-
×
OK
Figure (3) Blood transfusion
compatibilities according to the
blood group genotypes
Table 1: Rh Blood typing
compatibilities
Blood typing procedure
This is a regular clinical test where a drop of blood is mixed with pre-made
antisera containing certain antibodies (anti-A, anti-B or anti-D).
Formation of agglutination in the mixture indicates the presence of specific
antigen (depending on the antibody used), so the blood group can be identified.
Test:
- Disinfect your finger with 70% ethanol
- Use a blood lancet to obtain a small volume of blood
- Put 3 small separated spots of blood on clean tile, sterile microscopic slide.
- Add a drop of each antibody on the blood spots separately.
- Read the result after a while, agglutination means positive result for that
antibody used.
Figure 6: Blood grouping test: This figure shows the results of
adding Anti-A, Anti-B and anti-D antibodies on 3 spots of blood
separately. Agglutination is occurred with anti-A only, which
indicated that the type of this blood is A/Rh-