Anu Thomas: Understanding the ABO Blood Group System and Its Formation
Anu Thomas, Assistant Professor at Government Medical College, Kozhikode, shared a post on LinkedIn:
“Understanding the ABO Blood Group System and Its Formation
The ABO blood group system is one of the most important classifications in transfusion medicine.
It plays a critical role in ensuring safe blood transfusions and organ transplants.
This system is based on the presence or absence of specific antigens – A and B antigens – on the surface of red blood cells:
- Group A – Has A antigen and anti-B antibodies
- Group B – Has B antigen and anti-A antibodies
- Group AB – Has both A and B antigens and no antibodies
- Group O – Has no antigens but both anti-A and anti-B antibodies
How is it formed?
The ABO blood group is genetically determined and inherited from parents.
It is controlled by the ABO gene, which exists in three forms (alleles): A, B, and O.
- The A and B alleles are co-dominant, meaning both are expressed if present together.
- The O allele is recessive, meaning it only appears when both inherited alleles are O.
These genes influence the production of enzymes that modify the surface of red blood cells, leading to the formation of A or B antigens – or neither in the case of group O.
Why is it important?
Compatibility in the ABO system is crucial. Mismatched transfusions can lead to serious, even life-threatening reactions due to immune responses.
Understanding this system is fundamental in clinical practice, blood banking, and patient safety.”

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