This document summarizes the ABO blood grouping system. It describes how Karl Landsteiner discovered the A, B, and O blood groups in 1901. The system is based on the presence or absence of antigens called agglutinogens on red blood cells. People have antibodies against the agglutinogens that are not present on their own red blood cells. The genes that determine the ABO blood groups are located on chromosome 9 and are inherited according to Mendelian genetics. Blood type is determined by mixing blood cells with antisera that cause agglutination based on the antigens present.

1. ABO Blood Grouping System
Dr. Niaz Ahammed A.
1st yr M.D.S
Dpt of Prosthodontics

2. Contents
• Introduction
• Classification of blood groups
• Agglutinogens and Agglutinins
• Landsteiner’s Laws
• ABO blood grouping sysytem
• ABO antigens
• ABO antibodies
• Types of ABO blood groups
• ABO inheritance
• Determination of blood groups
• References

3. Introduction
• In 1901 Karl Landsteiner published his
discovery of a blood group system and he
grouped red cells into three categories; A,B
and O
• A fourth blood group , AB was discovered later
by Decastello and Sturli.
• Based on the type of antigen present or
absent, various blood grouping systems are
known

4. Classification
• Major blood grouping systems:
- ABO blood grouping system
- Rh (CDE) blood grouping system
• Minor blood grouping systems:
- MNS blood group system
- P blood group system
• Familial blood group systems:
- Only in a few families. Ex: Kell, Duffy, Lutheran,
Lewis, Deigo, Kidd etc.

5. Agglutinogens and Agglutinins
• Agglutinogens refer to antigens present on the
cell membranes of RBCs
• Agglutinins: antibodies against the
agglutinogens, are present in plasma
• Approximately 300 red cell antigens have now
been identified
• 18 blood group systems have been recognized

6. Blood grouping systems

7. Landsteiner law
• If an agglutinogen is present on the red cell
membrane of an individual the corresponding
agglutinin must be absent in the plasma
• If an agglutinogen is absent from the cell
membrane of RBCs of an individual, the
corresponding agglutinin must be present in
the plasma

8. ABO blood grouping system
• It was the first to be recognized and most
important
• Based on the presence of antigens called A and B
agglutinogens on the cell membrane of RBCs
• H antigen is also present usually in all individuals
but it is non- antigenic
• Almost everybody over the age of 6 months has
clinically significant anti-A and/or anti-B in their
serum

9. ABO antigens
• A,B and H antigens are glycoproteins and the differences in
terminal sugars determine the specificity of these antigens
L- fucose for H
L- fucose + N- acetyl-D- galactosamine for A
L- fucose + D- galactose for B
• 15 amino acids make up the protein backbone and four
sugars form side chains off this backbone
• A & B antigens are also present in many other tissues like
salivary glands, pancreas, kidneys, liver, lungs and testis and
in body fluids like saliva, semen and amniotic fluid
• H antigen- non antigenic

10. α- L – fucosyl transferase produced by H gene, attaches fucose and
yields H activity (group O)
α –N- acetyl- galactosaminyl transferase produced by A gene transfers
N-acetylgalactosamine and results in A activity
α- galactosyl transferase produced by B gene attaches galactose and
confers B activity

11. • Expression of ABH antigens on red cells is
controlled by genes that reside at two loci
• ABH antigens results from action of enzymes
(tranferases) on the appropriate precursor
substance
• The substrate is a product of H gene
(chromosome 19) and converted to A or B by
the action of A or B- transferases
(chromosome 9)

12. Variants of A and B antigens
• The principal sub groups of A are A1 and A2
• A1 constitute 80% of those in gp A
• A1 individuals agglutinated by Dolichos
biflorus lectin but not agglutinated by anti-H
lectin, Ulex europaeus
• A2 individuals are agglutinated by Ulex
europaeus
• Variants of B are less common, but are
recognized

13. ABO antibodies
• Individuals develop antibodies or agglutinins against A or B
antigen missing from their red blood cells
• Anti A /α agglutinin and Anti B/β agglutinins are present in
the plasma
• O people also possess an antibody referred to as anti-A,B
which reacts with either A or B red blood cells
• Bacteria with similar sugar moieties that confer A,B and H
reactivity provide antigenic stimulus
• Anti A and anti B are globulins of IgM type
• In individuals in O group, antibodies are of both IgM and
IgG classes
• α and β agglutinins act best at low temperature ( 5- 20
degrees Celsius) and are called as cold antibodies

14. • Two kinds of Anti-H also exist – Oh (Bombay)
group and other in group A1 and A1B
individuals
• ‘Bombay’ blood is very rare but the antibody
is active at 37 degree Celsius and only
‘Bombay’ blood can be transfused

15. Types of ABO blood groups
• Group A: A agglutinogen - B agglutinin
-A1 and A2 sub groups
• Group B: B agglutinogen- A agglutinin
• Group AB: A and B agglutinogen
- A1B and A2B sub groups
• Group O: both anti A and anti B in plasma

17. ABO inheritance
• The inheritance pattern of ABO genes follows
Mendalian autosomal genetics
• Four major alleles are located at the ABO locus on
chromosome 9
• 6 common phenotypes described- A1, A2,B,
A1B,A2B and O
• Most blood group genes are co-dominant (A and
B)
• O gene is a silent allele or amorph, with no
obervable expression

19. Co dominance: A state in which two diffrent alleles are
equally expressed
Silent genes or amorphs: those with no observable
expression

20. Determination of ABO blood grouping
• ABO blood group can be
determined by mixing one drop of
suspension of red cells with
a drop each of anti serum A
and antiserum B seperately on
a glass slide
• Anti serum A will cause agglutination of RBCs having
antigen A and anti serum B will cause agglutination
of RBCs having B antigen

21. Population distribution of Blood groups in India
A group
B group
AB group
O group

22. References
• Berne and Levy Physiology- Koeppan, Stanten
• Guyton and Hall text book of medical
physiology- Hall
• Text book of Physiology- A.K.Jain
• Haematology clinical and lab practise – Bick,
Bennet, Bynes, Cline
• Wintrobe’s clinical haematology- Less, Foester

23. Thank you