The ABO Blood Group System
PREPARED BY MR. ABHIJIT DAS
Discovery of ABO Blood Group
·
Discovered by: Karl Landsteiner in 1901.
·
Significance: He observed that mixing
blood from different individuals sometimes caused agglutination (clumping) of red blood
cells, which could be fatal
during transfusions.
·
He classified human blood into three
groups: A, B, and C (later renamed as O).
·
In 1902, von Decastello and Sturli,
colleagues of Landsteiner, discovered the AB blood group (which has both A and B
antigens on red cells and no antibodies in plasma).
Inheritance of ABO Blood
Group
· Controlled
by a single gene (ABO
gene) located on chromosome 9.
· There
are three alleles: IA,
IB, and i.
· IA
= codes for A antigen.
· IB
= codes for B antigen.
· i
= codes for no antigen (O).
· Inheritance
Pattern: Co-dominance.
Ø IA
and IB are co-dominant (both expressed when present together).
Ø i
is recessive.
Antiserum
· Antiserum
= Blood serum containing antibodies.
· Used to detect blood group
by identifying the presence or absence of
antigens on RBCs.
· Types:
Ø Anti-A serum:
contains antibodies against A antigen.
Ø Anti-B serum:
contains antibodies against B antigen.
Ø Anti-D serum:
used to detect Rh
factor.
Blood Grouping Techniques
(A, B, and D)
Principle:
- Blood
grouping is based on antigen-antibody reactions.
- Red
blood cells (RBCs) have antigens [A, B, or D(Rh antigen)] on their surface.
- The
plasma contains naturally occurring antibodies against the
missing antigens (in ABO system).
- When
antisera (anti-A, anti-B, anti-D) are added to a blood sample, agglutination
(clumping) indicates the presence of corresponding antigen.
Types of Grouping
1. Forward Grouping (Cell Grouping):
- Detects
A, B, and D
antigens on the surface of RBCs.
- Procedure:
- Mix
patient’s RBCs with:
- Anti-A
serum → detects A antigen.
- Anti-B
serum → detects B antigen.
- Anti-D
serum → detects D (Rh) antigen.
- Agglutination
indicates presence of the respective antigen.
|
Anti-A |
Anti-B |
Anti-D |
Interpretation |
|
+ |
– |
+ |
A
positive (A⁺) |
|
+ |
– |
– |
A
negative (A⁻) |
|
– |
+ |
+ |
B
positive (B⁺) |
|
+ |
+ |
– |
AB
negative (AB⁻) |
|
– |
– |
+ |
O
positive (O⁺) |
2. Reverse Grouping (Serum Grouping):
- Detects
antibodies
(Anti-A, Anti-B) in the patient’s serum.
- Procedure:
- Patient’s
serum is tested with known A and B red cells.
- No
reverse grouping is done for D antigen, as anti-D is not a naturally
occurring antibody.
|
Patient
Serum + A Cells |
+
B Cells |
Interpretation |
|
No
aggl. |
Agglut. |
A
group |
|
Agglut. |
No
aggl. |
B
group |
|
Agglut. |
Agglut. |
O
group |
|
No
aggl. |
No
aggl. |
AB
group |
Techniques of Grouping
1. Slide Method
- Principle:
Antigen-antibody reaction seen on a slide.
- Procedure:
- Place
drops of Anti-A, Anti-B, Anti-D on a slide.
- Add
patient’s blood to each.
- Mix
and observe for agglutination.
2. Tube Method
- Principle:
More controlled agglutination in test tubes.
- Forward
grouping: RBCs + antisera (Anti-A, Anti-B,
Anti-D).
- Reverse
grouping: Serum + known A and B cells.
- Use:
Hospital labs, routine testing.
3. Gel Card Method
- Principle:
RBCs are trapped in gel
if agglutinated.
- Procedure:
- Add
blood and antisera into gel microtubes (Anti-A, Anti-B, Anti-D).
- Centrifuge.
- Agglutinated
cells stay on top; non-agglutinated go to bottom.
- Pros:
easy interpretation.
- Use:
Modern transfusion labs.
4. Microplate Method
- Principle:
Reaction occurs in microplate
wells.
- Pros:
High-volume testing; semi or fully automated.
- Use:
Blood banks.