Introduction
Blood group systems are crucial in transfusion medicine, organ transplantation, and disease susceptibility.
The International Society of Blood Transfusion (ISBT) has classified red cell antigens into 25 blood group systems based on genetic and serological characteristics.
These antigens are present on the surface of red blood cells (RBCs) and determine a person’s blood type.
Genetic Basis of Blood Groups
Blood group genes are inherited in a Mendelian manner, meaning they follow predictable inheritance patterns from parents to offspring.
These genes are located on autosomes, which are the non-sex chromosomes.
Most blood group antigens are expressed in a co-dominant manner, meaning that if an individual inherits different alleles from each parent, both will be expressed equally.
Classification of Blood Group Systems
The ISBT recognizes 25 blood group systems broadly classified into major and minor systems.
Major Blood Group Systems
- ABO Blood Group System – The most clinically significant blood group system, determining compatibility for blood transfusions.
- Rh Blood Group System – Includes the RhD antigen, which is important in transfusion medicine and pregnancy.
Minor Blood Group Systems
- MNS Blood Group System
- P Blood Group System
- Lutheran Blood Group System
- Kell Blood Group System
- Lewis Blood Group System
- Duffy Blood Group System
- Kidd Blood Group System
- Diego Blood Group System
- Yt Blood Group System
- Xg Blood Group System
- Scianna Blood Group System
- Dombrock Blood Group System
- Colton Blood Group System
- Landsteiner-Weiner Blood Group System
- Chido/Rogers Blood Group System
- Hh Blood Group System
- Gerbich Blood Group System
- Cromer Blood Group System
- Knops Blood Group System
- Indian Blood Group System
- Ok Blood Group System
- Raph Blood Group System
Each blood group system has unique characteristics and clinical significance, particularly in transfusion reactions and hemolytic disease.
Key Concepts in Blood Group System
1. Alleles
An allele is an alternative form of a gene present at a specific locus on a chromosome. Blood group alleles determine the presence or absence of specific antigens on RBCs.
2. Co-Dominance
Most blood group system, including ABO and Rh, exhibit co-dominant inheritance. This means that both alleles inherited from parents are expressed equally in a heterozygous state.
3. Antigens
An antigen is a molecule or molecular structure present on the surface of RBCs. It triggers the immune system to produce antibodies when it is recognized as foreign.
4. Antibodies
Antibodies are proteins produced by the immune system in response to the presence of foreign antigens. They help neutralize or destroy incompatible RBCs in transfusion reactions.
Clinical Significance of Blood Group System
Blood group system are essential in blood transfusions, pregnancy, and organ transplantation.
A mismatch in blood groups can cause severe immune reactions such as:
- Hemolytic transfusion reactions – Occurs when incompatible blood is transfused, leading to RBC destruction.
- Hemolytic disease of the newborn (HDN) – Happens when a mother’s antibodies attack fetal RBCs, especially in Rh-negative mothers carrying Rh-positive babies.
- Graft rejection – In transplantation, mismatched blood groups can lead to organ rejection.
Conclusion:
The Role of Antibodies in Blood Group Systems
Antibodies play a critical role in maintaining immune defense by recognizing and neutralizing foreign substances, including mismatched RBCs.
In blood group systems, naturally occurring antibodies (such as anti-A and anti-B in the ABO system) and immune antibodies (such as anti-D in Rh-negative individuals) determine compatibility in blood transfusions and pregnancy.
Understanding blood group system is essential in transfusion medicine, prenatal care, and immunohematology.
Advances in genetic testing and blood typing continue to improve safety in transfusion practices and organ transplantation.
FAQ Section
How many blood group system exist?
The ISBT recognizes 25 blood group systems, including ABO and Rh.
Which blood group is the universal donor?
O-negative (O-) is the universal donor, compatible with all blood types.
Why are antibodies important in blood transfusion?
Antibodies detect foreign blood antigens, preventing transfusion reactions.
MCQ Quiz
Study Questions 1- Blood Bank – ABO and Rh Blood Group System
Study Questions 2- Blood Bank – ABO and Rh Blood Group System