Blood groups Flashcards
abo blood group system
ABO blood group system is a classification of blood depending upon presence of certain antigens called
agglutinogens on the surface of red blood cells. It was discovered by Karl Landsteiner in 1901.
Agglutinogens: There are 2 agglutinogens of ABO system, A and B. If A agglutinogen is present on the RBC of
an individual, he belongs to the blood group A; if B his blood group is B; if both are present blood group is AB
and if none is present, it is O blood group.
Blood group A is further divided into A1(has antigen A and A1) and A2(has only A antigen)
Chemistry: Agglutinogens A& B are mucopolysacharides and their specificity lies in the carbohydrate moiety).
Inheritance: Presence of these genes is decided by heredity. These are 3 corresponding genes A (which causes
formation of A antigen on RBCs) gene B (B antigen) and gene O (no antigens on RBCs)
Possible Genotypes and their phenotypes
AA A
AO A
BB B
B0 B
AB AB
OO O
Agglutinins of the AB0 system :-
Are the antibodies present in plasma which are capable of agglutinating (clumping) the RBCs containing
corresponding agglutinogen. They are of 2 type: Anti A and Anti B.
According to Landsteiner’s law “If a particular agglutinogen is present on RBCs of an individual (eg. A), the
corresponding agglutinin (i.e.Anti A) is always absent in plasma. If an agglutinogen is absent, corresponding
agglutinins are always present.
Composition of Blood groups
Blood Group agglutinogen Aggulutinin
A A Anti B
B B Anti ‘A
AB A and B Nil
O Nil Anti A & Anti B
Anti A and Anti B agglutinins are gamma globulins. They occur naturally and are formed due to exposure to A
and B antigens which are widely present in nature food, water, air etc.
Their titre is low at birth, starts rising from 2nd to 8th month and reaches peak between 8 to10 years.
significance of blood groups
Significance of Blood Groups :-
1. Blood transfusion: Knowledge of blood groups is essential to avoid mismatched blood transfusion. Before
transfusion donor’s cells are mixed with recipient’s serum (Major Cross Matching) and donor’s plasma with
recipient’s cells (minor cross matching) and examined for agglutination. Reaction between donor’s cells and
recipients plasma is more important. Hence, if donor’s cells do not contain any antigen( 0 group ), such a blood
can be given to any recipient (formerly called Universal donor). Similarly if there are no agglutinins in recipients’
plasma (AB group), he can receive blood from any group (Universal recipient). Mismatched blood transfusion
causes agglutination of donor’s cells by haemolysis leading to jaundice, haemoglobinuria, acute renal
shutdown, uremia and may cause death.
2. Medicolegal importance: Blood stains can be typed and matched with that of victim or assailant.
3. Paternity Test: To rule out paternity in cases of disputed parentage. For example if child’s blood group is ‘O’,
whatever may be mother’s group, father’s group can never be ‘AB’.
4. Identification of individuals and missing babies in maternity ward.
5. Racial studies: To trace common ancestry.
6. Anthropological studies.
7. Disease prevalence: Some blood groups have higher incidence of some diseases eg. Peptic ulcer in ‘O’,
Gastric cancer in ‘A’ group etc. Similarly Duffy negative persons are resistant to malaria.
8. Infertility Studies.
rh blood types
Rh group is a blood group system depending upon presence or absence of Rh antigen on red blood cells. It
was discovered by Landsteiner and Weiner in 1940 .
The name Rh is derived from its presence in the RBCs of Rhesus monkey .
Rh antigen (Rh factor) :- There are six types of Rh antigens C, c, D, d, E, e of these D (and C E) is strongly
antigenic, others have mild antigenicity . A person contains 3 of these antigens on his RBCs, one from each pair,
that is C or c, D or d, E or e. For Example, cDe or Cde or cdE etc.
Inheritance : Synthesis of these antigens on the RBCs is inherited from parents . There are 3 pairs of genes; Cc,
Dd, Ee. C,D,E are dominant and c,d,e are recessive genes. Each chromosome contains one gene from each pair.
Therefore Rh genotypes will be Cde/CDe etc.
Incidence: Rh positive- 95%, Rh negative- 5%
Rh antibodies :- are the antibodies capable of agglunating the cells containing Rh antigen . They belong to IgG
type of immunoglobulin and can cross the placenta . They are not present in plasma naturally like Anti A or
Anti B antibodies, but are formed in Rh negative persons only after exposure to Rh antigen in conditions like.
1.Transfusion of Rh positive blood into Rh negative person .2. In Rh negative mother having Rh positive fetus .
Clinical significance : Rh incompatibility can lead to
1.Erythroblastosis Fetalis or Hemolytic disease of Newborn
erythroblastosis fetalis
1.Erythroblastosis Fetalis or Hemolytic disease of Newborn :
Results from Rh incompatibility between mother and fetus where mother is Rh negative and fetus as Rh
positive . During first pregnancy, Rh antibodies are not formed, but at the time of parturition, there is some mixing of fetal blood with maternal blood and mother is exposed to Rh antigen (Sensitization). She, therefore,
starts forming Rh antibodies. In subsequent pregnancies with Rh positive fetus, the titre of antibodies increases
and they cross the placenta, enter the fetal circulation and agglutinate fetal red cells . Agglutination is followed
by hemoglobin which is converted into bilirubin by macrophages.
Clinical features :- 1. New born baby is severely jaundiced due to rise of bilirubin . 2. Bilirubin may be
deposited in the neurons of motor areas of brain causing mental impairment or motor dysfunction later in life
(Kernicterus) . 3. There is severe anemia and oxygen delivery to the cells is reduced . 4. There is strong
stimulation of erythropoiesis producing enlargement of liver and spleen. 5. Some of the immature forms of
RBCs i.e. erythroblasts appear in circulation . 6. Sometimes there is severe oedema (hydrops). 7. Death may
occur due to severe anemia.
Treatment :- Exchange transfusion in which about 400 ml of Rh negative ABO compatible blood is infused into
one arm slowly and Rh positive fetal blood removed from other arm . 6 weeks process
Prevention :-1. Administration of Anti-D Rh antibodies to mother immediately after delivery to prevent exposure
to Rh antigen (Desensitization) . 2. Proper marriage counseling .
