Download MBBS Practicals Physiology Blood Group

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Blood grouping is based on type of antigen
present on the red blood cells.

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There are more than 300 blood group
systems but ABO and Rh(Rhesus) are of
importance from clinical point of view.

Other blood group systems are MNS ,

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Lutheran , Kell , Lewis , Duffy , Kidd etc.

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Discovered by Karl Landsteiner in1900.

The red cells contain different types of

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Antigen(Agglutinogen) while plasma
contains antibody(Agglutinins)

Genes that control the system are present

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on chromosome 9


LANDSTEINER'S LAW

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If an antigen(Ag) is present on a patient's RBC,
the corresponding antibody(Ab) should not be
present in patient's plasma under normal
condition

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Methods of blood grouping:

1)Slide method

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2)Tube method


Tube method ?

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better method

but takes longer

Sample in tube with antiserum ---

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incubate it --- centrifuge it ---examine it
macroscopically and microscopically for
agglutination.

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REQUIREMENTS:

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1)3 slides
2)Antisera A , B

3) Blood samples

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PROCEDURE:

1)

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Take 2 clean slides and mark them 1, 2 .

2)

Put one drop of antisera A on slide 1 ,

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one drop of antisera B on slide 2.

3)

Add one drop of blood to each and mix

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well with stick

4)

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Wait for 5 min and observe.


OBSERVATION:

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If any agglutination occurs it is visible

with naked eyes as dark reddish clumps of
different sizes.

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If agglutination is minimal it can be

confirmed by examining it under
microscope.

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INTERPRETATION:
1)Agglutination with antisera A not with

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antisera B ? group A

2)Agglutination with antisera B not with

antisera A ? group B.

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3)Agglutination with both

antisera A and B ? group AB

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4)No agglutination in any slide ? group O



Universal donor ? blood group O as no

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Ag so no agglutination.

Universal recepient ? blood group AB

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as both A and B Ags present so
agglutination occurs in both as no
Abs present in serum.

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Rh TYPING

HISTORY:

1939 ? Levine and Stetson defined

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D antigen(Rh factor)

1949 ? Landsteiner and Weiner

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discovered anti Rh (named after
Rhesus monkey)


Rh TYPING

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Rh blood group system is second in

significance after ABO system.

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Genes that control the system are

present on chromosome 1

Consists of over 50 related Ags.

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Important genes are D,C,E,c,e.


All Rh antigen are controlled by 2 genes ?

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RHD gene? determines expression of D

RHCE ? encodes for C,c and E,e.

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RhD is a strong antigen (immunogenic) and

other antigen are less antigenic than D and
are of less clinical significance.

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Therefore , in practice Rh negative and Rh

positive depends on presence of D antigen on
the surface of red cells which is detected by

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strong anti-D serum.

Occasionally, Anti - D,C,E,c,e may develop

in case of pregnancy or transfusion.

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Rh positive

There is presence of D antigen.

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These individuals constitute 80% of

population.

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Rh negative:
There is absence of D antigen.These

individuals constitute 17% of

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population.

Cc and Ee antigen:
These are weak antigens and

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therefore risk of sensitisation is less
than that of D antigen.


Rh antibody:

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Unlike ABO system there is no
naturally occuring antibodies against
Rh antigens in Rh negative
individuals.

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Immune Abs:

Rh Abs develop against Rh Ag after
exposure to Rh Ags following

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transfusion or pregnancy.
But can be detected by enzyme
treatment or coomb
test(antiglobulin test)

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SIGNIFICANCE:

Rh incompartibility results in

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haemolytic tranfusion reaction.

Haemolytic disease of newborn.

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TECHNIQUES:

1) slide method

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2)Tube method


SLIDE METHOD:

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Place one drop of anti D on slide.

Add one drop of blood and mix
well with stick

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Wait for 5 min and observe.

RESULT:

Agglutination indicates Rh positive

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blood samples.


IMPORTANCE OF BLOOD

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GROUPING AND Rh TYPING:

In blood transfusion

Haemolytic disease of newborn.

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Paternity dispute
Medicolegal issues

Immunology,genetics,anthropology

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Susceptibility to various

disease(blood group O ? peptic ulcer
Blood group A ? gastric ulcer)

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Also known as compatibility testing.

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It is the most important test before

a blood transfusion is given.

The primary purpose of cross

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matching is to detect ABO
incompatibilities between donor and
recipient.

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This is carried out to prevent

transfusion reactions by detecting
Abs in recipient's serum.

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Two main functions of cross

matching test:
1)It is a confirm ABO compatibility

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between donor and recipient.

2)It may detect presence of
irregular Ab in patient's serum that
will react with donor RBCs.

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Cross matching test can be

1) major

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2) minor

MAJOR CROSS MATCH TEST:

Mixing the patient's plasma with

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donor RBCs.


MINOR CROSS MATCH TEST:

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mixing the donor's plasma

with patient's RBCs.

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SCREENING TESTS BEFORE BT:

Malaria
Syphilis

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HBV
HCV
HIV