Blood Groups 

The A,B, 0 Blood Group System 
The blood group of any individual belongs to one of the four major blood 
groups which are A,B,AB and 0. 
Now there are 6 phenotypes for blood groups among individuals. 
These phenotypes of blood groups are: At, A2, B, A1B, A2B, and 0 
-The locus (place) of the genes for the A-B-0 blood groups are present on the 
chromosome number 9. 
-There are at least 4 Alleles for the blood groups which are: A 1, A2, B and 0. 
– Group A2 is considered recessive to Group A 1• 
-Group 0 is considered recessive to both groups A and B. 
Group A Individuals 
– They have antigen A on their red blood corpuscles and anti B antibodies in their 
serum (Antigen A + Antibody b). 
-The major phenotype of group A is A. while their genotype is either AA or AO. 
-There are two subtypes for group A individuals which are the following:-
!. Subtype A1 ;_ndividuals. (Their blood groups are A1). 
2. Subtype A2 individuals. (Their blood groups are A2). 
Group B Individuals 
– They have antigen B on their red blood corpuscles and Anti A antibodies in their 
serum (Antigen B + Antibody a). 
-Their phenotype is B, while their genotype is either’B B or B 0. 
Group AB Individuals 
– They have antigen AB on their red blood corpuscles but no antibodies in their 
serum (Antigen AB +No antibodies). 
– Their major phenotype is A B, while their genotype is either A 1 B or A2 B. 
-There are 2 subtypes of group AB Which are: 
1. Subtype A 1 B individuals. 
2. Subtype A2 B individuals.
Group 0 Individuals 
– They have no antigens on their red blood corpuscles, while their serum contains 
anti A and anti B antibodies (No antigens+ Antibodies a and b). 
-Their phenotype is 00, while their genotype is 00. 
Medical Importance Of Blood Groups 
Blood groups are very important to be known. They are essential for blood 
transfusion and for medicolegal applications. 
Blood Transfusion 
In blood transfusion the serum of the donor is greatly diluted by the serum of 
the recipient. The danger in blood transfusion between individuals is supposed to 
come from the liability of the R.B.Cs of the donor to be agglutinated by the serum 
of the recipient So group 0 which has No antigens on its R.B.Cs., is a universal 
donor; and group AB which has No antibodies in its serum is a universal 
The donor’s blood must be free from diseases such as: AIDS, Syphilis, 
Malaria and viruses of infective hepatitis (Liver disease viruses). 
Co-Dominant Genes 
N.B.: It has been found that the A-B-AB-0 blood groups are inherited by 
co-dominant genes. 
Example: a gene of group A is dominant for a gene of group 0, and a gene of 
group B is dominant for a gene of group 0. Thus a gene of group 0 is recessive to 
both genes of group A and B. 
However, neither A nor Bare dominant to one another, when genes A and B 
are present together, they produce their effects (Co-dominant genes). 
Examples: If the father is of group A and the mother is of group B, one of 
their children may be of group AB. 
Medico – Legal Importance Of Blood Groups 
Medicolegal applications, of blood grouping is important when the blood 
groups of the parents and the offsprings are known, it is sometimes possible to 
prove that these offsprings are not from these parents. 
N.B.: There are other less important blood subgroups as: MNSs, P, Kell, Duffy 
Lewis and the Rh blood group systems.
The Rhesus Factor (Rh Factor) 
The Rhesus (Rh) Blood Groups In Man: 
– The Rhesus factor is an antigen which was first discovered in special species of 
monkeys called Rhesus monkeys and was named after them. 
-This Rhesus antigen (Rh) is found on the red blood corpuscles of about 85% of 
human individuals. 
– Persons whose blood contains the Rh antigen are called Rh+ (positive) 
– It was suspected that the Rh blood group is determined by a pair of alleles: D and 
d producing three genotypes: DD, Dd and dd. 
– Rh + positive individuals are either homozygous with DD or heterozygous with 
-Persons whose blood is free from these Rh antigens are called Rh- (negative) 
individuals. They contain dd alleles. 
-If an Rh- negative individual is injected (during blood transfusion) with an Rh + 
positive blood, he will develop anti Rh (antibodies) in his blood plasma. 
– An Rh – negative woman may form anti Rh Antibodies in her plasma during her 
delivery to an Rh +positive foetus. 
– If a man with an Rh positive blood, gets married with a woman with an Rh 
negative blood, the children may inherit the Rh positive blood from their father. 
The first child will come without complications but during his labour some foetal 
blood (Rh positive) pass to the mother’s circulation. The mother’s blood will 
start to form anti Rh antibodies. In the next pregnancy these antibodies will 
cross the placenta to be mixed with the foetal blood of the second foetus causing 
haemolysis of his blood and intra-uterine foetal death. This condition is called 
Erythroblastosis Foetalis. For the treatment of this case, these pregnant mothers 
should be injected with a preparation of Anti D (Anti Rh) in the last 2 months 
of her pregnancy and with another injection immediately after each delivery or 
each abortion. 
The Following are the main types of Haemolytic Diseases OF Newborn (HDN) 
1- Rh Incompatibility. 
2- ABO blood group incompatibility. 
3- Kell blood group system.
Blood is a viscous fluid, formed of: Blood Plasma (55%) and Blood cells 
Types of Blood Cells And Their Average Number In The Human Body:-
1. Red Blood Corpuscles or RBCs or Erythrocytes: about 4.5 to 5.5 millions per 
cubic millimetre. 
2. White Blood cells or Leucocytes: about 4000 to 11000 per cubic millimetre. 
3. Blood Platelets or Thrombocytes: about 150,000 to 400,000 per cubic 
The Major Functions Of Blood Are:-
1. Transport of oxygen, nutritive substances and hormones to all tissues. 
2. Removal of carbon dioxide and waste products through the lungs, Kidneys and 
sweat glands. 
3. Control of body temperature. 
4. Maintenance of acid-base balance. 
5. Protect the body against infections through the action of leucocytes.
Red Blood Corpuscles = RBCs 
Number Of RBCs 
-In males: The number varies from 5 to 5.5 millions per cubic millimetre: 
– In females: The number varies from 4.5 – 5 millions per cubic millimetre. 
The number is less in females due to loss of blood during menstruation. 
Abnormalities in the Number of RBCs: Decrease in the number of RBCs is 
known as Anaemia. Increase in their number is known as Polycythaemia. 
Anaemia: It is either a decrease in the number of RBCs (oligocythaemia) or due to 
a decrease in haemoglobin content of RBCs. 
Causes and Types of Anaemias 
1. Deficiency Anaemia, deficiency of these elements may result in anaemia: iron, 
copper, proteins, hormones, vitamin C and vitamin BI2. 
2. Haemorrhagic Anaemia, as haemorrhage from nose, gums, piles and wounds. 
3. Haemolytic Anaemia, when there is an excessive destruction of RBCs as in 
certain congenital abnormalities of the cell membrane as in Spherocytosis; OR 
deficiency of enzymes as in Favism; OR Presence of haemoglobin F as in 
Thalassemia, OR presence of haemoglobin S as in Sickle cell anaemia. 
4. Aplastic Anaemia; When the bone marrow (in which RBCs are formed) is
congenitally abnormal. or if it is partially destroyed by X-ray or by antibiotics. 
Polycythaemia or increase in the number of RBCs above 6 millions as in 
hypoxia or in low oxygen tension as in high altitudes. also in heart and lung 
Shape Of RBCs 

They are rounded, non-nucleated 
biconcave discs. In slow blood stream  
and in blood fi lms, RBCs adhere 
together due to their surface tension showing a rouleaux a ppear·ance. 
Abnonnal Shapes of R. B. Cs 
In certain anaemias RBCs may be pear-shaped (poikilocytes) or may be 
biconvex (spherocyte.-,) or may be oval in shape (ovalocytes). 
Diameters of RBCs 
Normal diameter of an RBC is 7.5 microns and the normal thickness is 1.9 
microns at the periphery and 1.1 microns at the centre of RBC. 
Abnormalities In The Diameters Of RBCs 
1. In Macrocytic Anaemais there is an increase in the diameters of RBCs. 
2. In Microcytic Anaemias there is a decrease in the diameters of RBCs. 
Structure of RBCs 
– RBCs are acidophilic in staining because their Hb is a basic protein. 
– RBCs have no nuclei and no organelles except their cell membranes. 
– RBCs have on their surfaces the antigens of blood groups and of Rh factor. 
– RBCs contain haemoglobin , its concentration is about 12-16 gm% (per 100 cc blood). 
– RBCs contain glycolytic a nd carbonic anhydrase enzymes. 
Types of Haemoglobins (Hb) 
I . Normal adult Hb. A: present in 9<1% of normal individuals. 
2. Foetal (Hb, F) : present in Thalathcmia which is a kind of anaemia. 
3. Haemoglobin S: present in sickle cell anaemia in which Hb form a crescent in RBC. 
-They are immature RBCs which contain RNA, Their diameters are large. 
-Their percentage in normal blood is not more than 2%. 
– Their number increase in certain anaemia. They can be stained with cresyle blue. 
Colour Of RBCs 
– RBCs a r·e greenish yellow in colour· due to presence of Haemoglobin (Hb). 
A drop of blood appears red due lo overl apping of RBCs. When the Hb% is 
normal, the red blood corpuscles are called Normochromic.
Abnormal Colour Of RBCs 
a) RBCs with less Hb% than normal are pale and are called hypochromic. 
b) RBCs with more Hb% than normal are called hyperchromic. 
c) In target cell anaemia, the Hb is concentrated in the centres of RBCs 
forming a central coloured mass and a peripheral pale ring (like the target). 
Contents Of RBCs 
– They are not true cells, they have neither nuclei nor organoids. 
– They are surrounded by plastic cell membranes formed of lipoprotein. 
– RBCs contain a cytoskeleton network formed of protein called Spectrin. 
– The RBCs are filled with haemoglobin (Hb). Haemoglobin combines with 
oxygen to form oxyhaemoglobin, it goes to the tissues to supply them with 
oxygen. It also transports carbon dioxide from the tissues to the lung. 
Rupture of the cell membrane and loss ofHb outside the R.B.Cs is known as 
haemolysis which may be caused by: acids, alkalies, malarial and bacterial 
toxins, snake venom, hypotonic solution and incompatible blood transfusion. 
Osntotic Pressure: normally the osmotic pressure of RBCs is 0.9% saline. If 
the RBCs are exposed to hypertonic solution (2%) crenation will occur, while if 
they are exposed to hypotonic solution swelling, rupture and haemolysis will occur. 
Life Span Of RBCs 
RBCs can live for about 4 months. The life time can be calculated by 
isotopes. Old RBCs are destroyed by the phagocytic cells in the liver, spleen 
and bone marrow. Their Hb can be changed to bile pigments and 
haemosiderin granules. 
Adaptation Of The Structure Of RBCs 
In Order To Perform Their Functions 
1. The cell membrane of RBCs is plastic. It allows RBCs to change their shape. 
RBCs are in the form of corpuscles with rounded edges which facilitate their 
passage inside narrow blood capillaries. 
2. The biconcave surfaces of RBCs increase their surface areas, through these 
surfaces, gaseous exchange (02 + C02) takes place. 
3. The cell membrane of RBCs is formed of lipoprotein, it is highly selective, 
it allows easy exchange of carbon dioxide and oxygen through it. 
4. There is neither nuclei nor cell organoids in RBCs, this prevents RBCs from
reproduction. Their absence also allows free space for haemoglobin. 
5. The main function of RBCs is to enclose haemoglobin, this haemoglobin is 
formed of a protein (globin) and an iron containing pigment (haem). 
Haemoglobin combines easily with oxygen to form oxyhaemoglobin which 
goes to the tissues to supply them with oxygen. Haemoglobin also plays a role 
in controlling the hydrogen ion concentration of the blood. Haemoglobin can 
only do these functions when it is present inside the RBCs. 
6. RBCs are rich in carbonic anhydrase enzyme which facilitates combination 
of haemoglobin with C02 and to get rid of this C02 through the lung.
The Haemocytometer

Red Blood C{)unt 
RBCs, leucocytes and blood platelets arc counted by the haemocytometer 
which is formed of: a diluting pipette and a counting slide. 
The diluting pipette for RBCs has a large bulb. The pipette is graduated as 
0.5 at the middle of the tuble, 1.0 below the bulb I 01 above the bulb. 
The bulb contains a piece of red glass to mix the blood with the diluting fluid. 
The counting slide has a depression on its centre with a depth= 1/lOmm. 
The square erea of the base of this depression= one square millimetre which 
is divided by 20 lines vertically and another 20 lines horizontally. so it 
contains 400 small squares.
Thus, the surface area of each small square = Length X Width= 
= _1_ X _1 = _1 mm2 
20 20 400 
The volume of each small square = Length X Width X Depth= 
l 1 l 1 
= 20 X 20 X lo = 4000 mm3 
This means that, the volume of one cubic millimeter = 4000 times the volume 
of each small square 
To facilitate counting, each 16 small squares are grouped into one large square. 
Steps Of RBCs Counting 
1. Clean the thumb with alcohol and leave it to dry in air. With a sterilized needle, 
Prick the thumb, in order to bring a drop of blood. 
2. Suck the blood with the diluting pipette till the mark 0.5 is reached. Rapidly 
dilute the blood by sucking saline till the mark 101 is reached, and shake well to 
mix the blood with saline (the blood is now diluted 200 times). 
3. Blow out few drops from the pipette, then put a drop of the diluted blood on the 
depressed area of the counting slide, cover with a cover-glass and count the 
number of R.B.Cs under the high power of the microscope. They appear as 
greenish yellow circles. 
4. Count the total number of R.B.Cs which is present in 5 large squares (Each 
large square contains 16 small squares). 
5. Calcuate the number of R.B.Cs per cubic millimetre using this equation. 
If the total number of RBCs which is counted in one small square = N. 
Then, the total RBCs count= N X 4000 X 200 = ? millions per cubic millimetre. 
But if the total number of RBCs which is counted in 5 large squares = N 
So the total number of RBCs= N X ~~ ~ 200 =?millions per cubic millimetre 
N.B. In clinical laboratories, they do the previous steps, they count the number of 
RBCs in 5 large squares, this obtained number is then multiplied by 10.000 in 
order to get out the number of R BCs per cubic millimetre. 
Nowadays, the laboratories usc electronic apparatus which counts the different 
types of blood cells automatically.
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