Bombay (HH) Blood Group: Rare Blood Type Basics

The Bombay Blood Group is one of the rarest blood types in the world. It was first discovered in 1952 in Mumbai, formerly known as Bombay, India. Scientifically known as the hh blood group, this rare phenotype lacks the H antigen, which is essential for the formation of A and B antigens in the ABO blood group system. Because of this unique characteristic, individuals with the Bombay Blood Group cannot receive blood from any other ABO blood group, including O. This topic is important for students, medical aspirants, and especially NEET candidates as it is closely related to genetics, blood grouping, and immunology.

What is the Bombay Blood Group?

The Bombay Blood Group is a rare blood type in which the red blood cells do not have the H antigen. In the normal ABO blood group system, the H antigen acts as a precursor for the formation of A and B antigens. If the H antigen is absent due to a genetic mutation, even if a person has genes for A or B blood group, those antigens cannot be expressed.

As a result, individuals with the Bombay Blood Group appear to have O blood group in routine testing. However, they produce anti-H antibodies in their plasma, which makes their blood incompatible with all other ABO blood types.

Discovery of the Bombay Blood Group

The Bombay Blood Group was first identified in 1952 by Dr. Y. M. Bhende and his team in Mumbai, India. During routine blood testing, they found patients who were classified as O group but could not receive O group blood. Further investigation revealed the absence of the H antigen, leading to the identification of this new and rare blood phenotype.

Genetic Basis of Bombay Blood Group

The Bombay Blood Group is caused by a mutation in the FUT1 gene, which is responsible for the production of the H antigen. The inheritance pattern is autosomal recessive.

• Individuals must inherit two recessive h alleles (hh) to express the Bombay phenotype.
• People with genotype HH or Hh produce the H antigen normally.
• Only individuals with hh genotype lack the H antigen.

This concept is important in NEET under the topics of Mendelian inheritance and blood group genetics.

Comparison Between ABO Blood Group and Bombay Blood Group

The key difference is the absence of the H antigen in the Bombay Blood Group, which makes it incompatible even with O blood group.

Clinical Significance

The Bombay Blood Group has great importance in blood transfusion medicine. If a person with this blood type receives blood from any other group, including O, a severe hemolytic transfusion reaction can occur due to the presence of anti-H antibodies.

• Extremely rare, approximately 1 in 10,000 in India.
• Even rarer globally, about 1 in 1,000,000.
• Requires special blood bank identification and registry.
• Family members are often screened for compatibility.

Importance in Blood Transfusion

Before transfusion, detailed blood grouping and cross matching must be done. Advanced serological tests are required to detect the absence of H antigen. Awareness among doctors and blood banks is crucial to prevent life threatening reactions.

How is Bombay Blood Group Detected?

Routine ABO typing may incorrectly label Bombay phenotype as O group. Therefore, additional testing is required.

1. Forward grouping to detect A and B antigens.
2. Reverse grouping to check for anti-H antibodies.
3. Testing with anti-H lectin to confirm absence of H antigen.

These steps help differentiate between O blood group and Bombay Blood Group.

Key Points for NEET Preparation

• Bombay Blood Group is also called hh phenotype.
• It lacks H antigen due to mutation in FUT1 gene.
• Inheritance pattern is autosomal recessive.
• Individuals have anti-H antibodies in plasma.
• They can receive blood only from another Bombay Blood Group individual.

Conclusion

The Bombay Blood Group is a rare and medically significant blood type characterized by the absence of the H antigen. Discovered in Mumbai in 1952, it follows an autosomal recessive inheritance pattern and poses serious challenges in blood transfusion. Understanding this topic is essential for students preparing for NEET, as it connects concepts of genetics, blood grouping, and immunology. Proper identification and awareness can save lives and ensure safe transfusion practices.