BLOOD GROUPS AND Rh FACTOR

• Blood is defined as a red color fluid that circulates through the vascular system in humans and other vertebrates, carrying nutrients and oxygen, and waste products including carbon dioxide from all parts of the body.

• Blood contains the blood cells which are called formed elements (RBC, WBC, Platelets), and the fluid matrix is known as plasma.

 

BLOOD GROUPS –

• A blood group is a categorizing of blood, based on the presence and absence of antibodies and inherited antigenic substances on the surfaces of red blood cells.

• Various types of grouping of blood have been done. From all of them, two are widely used all over the world –

1. ABO system

2. Rh factor system

 

ABO GROUPING –

• ABO grouping is based on the presence or absence of two surface antigens namely, An antigen and B antigen on the surface of RBCs.

(ANTIGENS ARE THE CHEMICALS THAT CAN INDUCE IMMUNE RESPONSE).

• LANDSTEINNER’S LAW – If a particular antigen is present in the RBCs of a person, the corresponding antibody must be absent in the serum and vice versa.

• Based on the presence or absence of antigen A and antigen B, blood is classified into 4 groups –

1. ‘A’ group

2. ‘B’ group

3. ‘AB’ group

4. ‘O’ group

Antigen and antibody present in ABO blood groups –

 

GROUP

ANTIGEN IN RBC

ANTIBODY IN SERUM

 

A

A

Anti-B(β)

 

B

B

Anti-A(α)

 

AB

A and B

No antibody

 

O

No antigen

Anti-A and Anti-B

 

 

‘A’ group has subdivided into two namely ‘A1’ and ‘A2’. Similarly, the ‘AB’ group has two subgroups namely ‘A1B’ and ‘A2B’.

 

SIGNIFICANCE OF ABO GROUPS IN BLOOD TRANSFUSION –

• The one who gives blood is called ‘donor’ and one who receives the blood is called ‘recipient’.

• While transfusing the blood, an antigen of the donor and the antibody of the recipient are considered.

• RBC of ‘O’ group has no antigen and so it can give the blood to any blood group persons and the people with this blood group are called ‘universal donors’.

• The plasma of AB group blood has no antibody. People with the AB group can receive blood from any blood group persons. So, people with this blood group are called ‘universal recipients’.

 

Blood matching is a laboratory test done to determine the blood group of a person.

 

 

Rh GROUPING –

• Rh factor is an antigen present in RBC.

• It was first discovered in Rhesus monkey and hence the name ‘Rh factor.

• The persons having Rh antigen on their RBC are known as ‘Rh positive’ and those without Rh antigen are called ‘Rh negative’.

• Among the Indian population, 85% of people are Rh-positive and 15% are Rh-negative.

• A Rh-negative person, if exposed to Rh-positive blood, will form specific antibodies against the Rh antigens. Therefore, the Rh group should also be matched before transfusions.

• A special case of Rh incompatibility has been observed between the Rh-negative blood of a pregnant mother with Rh-positive blood of the fetus.

Rh antigens of the fetus do not get exposed to the Rh-negative blood of the mother in the first pregnancy as the two types of blood are well separated by the placenta.

However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the Rh-positive blood from the fetus.

In such cases, the mother starts preparing antibodies against Rh antigen in her blood. In the case of her subsequent pregnancies, the Rh antibodies from the mother (Rh-negative) can leak into the blood of the fetus (Rh-positive) and destroy the fetal RBCs.

This could be fatal to the fetus or could cause severe anemia and jaundice to the baby. This condition is called erythroblastosis foetalis.

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