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Blood: ABO and Rh Blood Groups, Blood Typing, Blood Incompatibility Related Diseases, Practice Problems and FAQs

Have you heard about blood groups? 

Once I went to donate my blood to my relative in a hospital where I had to undergo a blood test.

blood test

My blood group was written in the report and it was O. Doctor said that I can donate my blood to anyone. I did not understand what he was trying to say.

Why was the blood group checked? Does it make any sense to do such practice ?

Yes ! Of course.

During the blood transfusion from donor to recipient, it was observed that not every time it was successful. In some situations immediately after transfusion or a little bit later, the blood of the recipient showed hemolysis of RBCs or sometimes agglutination of RBCs. This caused the death of the recipient due to an antigen antibody reaction. 

Thus it was clear that the blood of human beings differs in certain aspects though it appears to be similar. You know, there are about 40 different blood groups. But only two blood groups named ABO blood group and Rh blood group are clinically significant.

Let’s take a deep dive into the details of blood groups. 

Table of Contents

Introduction to Blood Grouping and Blood typing

Blood is the fluid connective tissue. It is also the most important component of the circulatory system. Blood of different individuals have different antigenic and immune properties which depend upon the type of antibodies in their bodies. The components of blood are the same for all humans, but they possess various blood types. 

Blood Type

It is based on certain proteins that are present on the red blood cells. These proteins are called antigens. The blood grouping system is very important in blood transfusion. Our immune system recognises another blood type as foreign and attacks it, if introduced in the body. It causes a transfusion reaction. 

Antigens and Antibodies


They are the portions of foreign material that invade the body. They can be proteins, peptides, and carbohydrates. Every individual contains self antigens also, which are already present on the different cells in the body including RBCs. 

The two antigens present in human RBCs are carbohydrate antigens. They are known as antigens A and B. Antigens are present on the surface of RBCs. Based on these two antigens, the ABO blood group is divided into four types as follows: 


  • A
  • B
  • AB 
  • O

types of blood group


Antibodies are proteins found in blood plasma. They are part of our body's natural defences or immune system. Antibody (Ab) is also known as immunoglobulin (Ig). They recognise foreign substances known as antigens and alert the immune system by binding with the antigens using the antigen binding sites. Other cells of the immune system are able to recognise the antigens bound to antibodies and destroy them.


Major Blood Groups

During the blood transfusion, the two most important blood group systems examined are as follows:

  • ABO blood group system
  • Rhesus or Rh blood group system

ABO Blood Group System

ABO blood grouping is a system based on the presence or absence of two surface antigens namely A and B on the RBCs. The plasma of different individuals contains two natural antibodies named ‘anti-A and anti-B’. This system was reported for the first time by Karl Landsteiner

Types of Blood Groups in ABO Blood Group System

The ABO grouping system is classified into four types based on the presence or absence of antigens on the red blood cells surface and antibodies in the plasma. They are as follows:

  • A blood group – It contains antigen A on the surface of RBCs and anti -B in the plasma.
  • B blood group – It contains antigen B on the surface of RBCs and anti-A in the plasma.
  • AB blood group – It contains both A and B antigens on the surface of RBCs and no antibodies (neither A nor B) in the plasma.
  • O blood group – It contains neither A nor B antigen on the surface of RBCs, but possesses both antibodies anti-A and anti-B in the plasma. 

blood grouping

Compatibility of ABO Blood Groups During Transfusion

Before transfusion, the blood of the donor needs to be carefully matched with the blood of the recipient. This is called a blood compatibility test. It is conducted in a medical laboratory for identification of potential incompatibilities between the blood types for blood transfusion. This can prevent severe problems of clumping and destruction of RBCs after blood transfusion. 

As shown in the below table, individuals with blood group O are called as universal donors, as the ‘O’ blood can be donated to persons with any other blood groups. The individuals with blood group AB are called as universal recipients as the ‘AB’ blood can accept blood from persons with any blood groups. 

blood group compatibility

Rh Blood Group System

The Rh blood group system is one of the prominent blood grouping systems. About two-thirds of the population normally contains the third antigen called Rh factor or Rh antigen on the surface of their red blood cells. This antigen was discovered by Landsteiner and Weiner in the red blood cells of rhesus monkeys and human beings. 

People who have Rh antigen in their RBCs have positive blood groups or are termed as Rh positive. People who do not have this antigen in their RBCs have negative blood groups or are termed as Rh negative. Thus the need for compatibility between donor and recipient individuals is crucial in this case as well.

Compatibility of Rh Blood Groups During Transfusion

Rh-negative Person Receiving Rh-positive Blood

In this case, the Rh antigen is foreign to the recipient. As the donor’s blood enters the recipient’s body, it generates specific antibodies known as anti-Rh antibodies. Once the anti-Rh antibodies bind with the antigen Rh on the donor RBCs, the immune cells of the recipient attack the foreign RBCs. It results in the destruction of RBCs. The destruction of RBCs leads to blood clotting in the blood vessels. This can lead to death in severe cases. 


Rh-positive Person Receiving Rh-negative Blood

As there are no antigens on the donor’s blood cells in this case, the antibodies will not be generated in the recipient. Hence, a blood transfusion will be allowed as there will be no reaction.

rh positive

Erythroblastosis Foetalis

It is a life-threatening disease of a foetus or a newborn in which the immune system of the mother produces antibodies against the red blood cells of the infant. It is also called the haemolytic disease of the newborn. It is a type of Rh incompatibility observed between the Rh- blood of a pregnant mother and Rh+ blood of the foetus. 

During the first pregnancy, the Rh antigens of the foetus do not get exposed to the Rh- blood of the mother as the two bloods are separated by the placenta. But during the delivery of the first child, there is a possibility of exposure of the maternal blood to the Rh+ blood of the newborn. 

In this type of a case, the mother’s body immediately starts preparing antibodies (anti-Rh factor) against Rh antigen in her blood. These antibodies do not affect the first baby since it was already delivered. But it results in the destruction of the red blood cells of the foetus in the subsequent pregnancies, as these antibodies leak into the blood of the foetus and destroy the foetal RBCs.

The destruction of RBCs happens because of the Rh incompatibility between the mother and the foetus and may result in the foetus to suffer from severe anaemia, brain damage or even death in extreme cases. This can be prevented by injecting anti-Rh antibodies to the mother normally. This can be done within 74 hours after the delivery or the termination of pregnancy. RhoGAM is the common type of injection used to treat Rh incompatibility occurs during pregnancy.

erythroblastosis fetalis

Practice Problems of Blood

Question 1. The transfusion of AB blood may be normally given to a person who has blood type __________________.

(a) A

(b) O

(c) B

(d) AB

Solution: Person with blood group AB is a universal recipient which means it can take blood from a person with any blood group, but it can donate its blood to only people with AB blood group. Hence option d is the answer. 


Question 2. Red blood cells that do not contain either A or B antigens on their surface are normally found in the person with blood type ___________.

(a) A

(b) O

(c) B

(d) AB

Solution: Person with blood type O does not have any antigens on RBC surfaces but both the antibodies are found in the blood plasma. Thus it can donate blood to people with any blood type. Hence option b is correct.

Question 3. A person with type A blood will have antibodies _____________.

(a) anti-A, but not anti B

(b) neither anti-A nor anti B

(c) both anti-A and anti B

(d) anti-B, but not anti-A

Solution: Person with type A blood possesses A antigens and anti-B antibodies. Hence option d is correct.

4. The antigens for ABO and Rh blood groups are present on _______________.

(a) plasma

(b) white blood cells

(c) red blood cells

(d) platelets

 Solution: Red blood cells are the common type of blood cells involved in the transport of oxygen throughout the body. They possess the antigens for ABO and Rh blood groups on their surface. Hence the correct option is c. 

FAQs of Blood

Question 1. Why is blood group O negative considered as the universal donor?

Answer: A person having O negative blood group lacks all the antigens. But they have antibodies, Anti-A and Anti-B in their plasma against A and B antigens respectively. So they can donate blood to people with any blood group without complications.

Question 2. Is it possible to have a parent and the foetus with different Rh factors?

Answer: Yes, it is possible to have a parent and the foetus with different Rh factors. For example, the mother may be Rh negative but the baby could be Rh positive if it inherits the Rh antigen from the father.

Question 3.What do you know about the golden blood type?

Answer: The golden blood type is the Rh null blood group which contains no Rh antigen on the RBCs. This is considered as the rarest blood group in the world. Only less than 50 individuals have been identified with such blood groups.

Question 4. Which blood type is a universal donor O + or O- ?

Answer: Although the blood type O + can donate blood to all positive blood types (A+, B+, AB +, and O +), it is not a universal donor. Blood type O- is considered as the universal blood donor as they can donate blood to all other blood groups. It also results in a lower risk of causing serious transfusion reactions. 


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