Why is Blood Group O called Universal Donor?

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Ask BioTecNikaWhy is Blood Group O called Universal Donor?
Prabha Prabha asked 1 year ago

A blood group people have A antigen and B antibody
B blood group people have B antigen and A antibody
AB blood group people have both the A and B antigen and none of the antibody
O blood group people have both A and B antibody and none of the antigen
AB blood group people are called as universal accepter and O group people are called as universal donor
My doubt is , if O group blood is transfused to AB group people , both the antigen and antibody that is both the antibody in O blood react with both the antigen in the AB blood results in the agglutination…….this is same to A and B blood group people when O blood is transfused to them…….
Then why O group is called universal donor and AB group is called universal accepter????

1 Answers
Ria Roy Staff answered 1 year ago

The ABO Blood Grouping System.

There are mainly four blood group types. They are  A, B, AB, and O blood groups. Anyone’s blood group is solely determined by the genes that are inherited from your parents. Each of these blood groups can be either have RhD positive or RhD negative group, which means in total there are eight main blood groups.

Antibodies and antigens

Our Blood is made up of red blood cells or Erythrocytes, white blood cells or leukocytes, and platelets in a liquid called plasma. Blood groups are identified by antibodies and antigens in the blood. Antibodies are the proteins found in plasma and they are part of one’s body natural defenses or say part of humoral immunity. Antibodies recognize foreign substances and pathogens such as germs. They alert your immune system, which in turn destroys these foreign particles. Antigens are protein molecules found on the surface of RBCs.

The ABO system blood grouping system:

There are four main blood groups defined by the ABO system:

  • blood group A – which has A antigens on the red blood cells with anti-B antibodies in the plasma
  • blood group B  – which has B antigens with anti-A antibodies in the plasma
  • blood group O  – which has no antigens, but both anti-A and anti-B antibodies in the plasma
  • blood group AB  – which has both A and B antigens, but no antibodies


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Blood group O is the most common blood group. Receiving blood from the wrong ABO group can be life-threatening and agglutination. For example, if someone with a blood group A blood is given a group B blood then their anti-B antibodies will attack B antigen and cause blood agglutination. And this is the reason why group A blood must never be given to someone whose blood group is B and vice versa. Group O red blood cells don’t have any of the antigens. i.e A & B antigens are absent. Blood from the O group can be safely given to any other group.

The Rh system

Red blood cells have another antigen sometimes. The positive or negative factor is based on the presence and absence of this protein. That protein is known as the RhD antigen. If the RhD protein is present in one’s blood group then he/she is RhD positive. If RhD protein is absent in one’s RBCs then his blood group is RhD negative which simply means you can be one of eight blood groups: i.e,

  • A positive (A+)
  • A negative (A-)
  • B positive (B+)
  • B negative (B-)
  • AB positive (AB+)
  • AB negative (AB-)
  • O positive (O+)
  • O negative (O-)

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Blood Group test:

To find the blood group, blood can be mixed with different antibody solutions. For example, the solution contains anti-A antibodies and you have A antigens on your cells (you’re blood group A), it will result in blood clumping or clot. If the blood doesn’t form agglutination or clumps to any of the anti-A or anti-B antibodies then you can say that the blood group is  O.  Blood transfusion is the process where blood is taken from one person and given to another. So before Blood transfusion, your blood will be tested against a  blood sample of donor cells to find whether that is compatible. If there’s no reaction or clumps occurring then the donor blood with the same ABO and RhD type can be used.


Pregnant women are always given a blood group test. This is because if the mother is RhD negative but the child has inherited RhD-positive blood from the father, it could cause complications if left untreated. This is the reason for Erythroblastosis fetalis. RhD-negative women who are carrying should always only receive RhD-negative blood. Anyone can donate blood if they are fit and healthy should weigh at least 50kg He/She should be between are 17-66 years old and have given blood in the last two years.


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