Blood Groups-ABO Blood Group and Rh Group System
Blood groups are classified mainly by the ABO and Rh systems, based on antigens present on red blood cells and antibodies in plasma. The ABO system with the four types being A, B, AB, and O, and the Rh factor, which could either be positive or negative. Correct blood typing is essential for safe transfusion, organ transplantation, and understanding immune responses. This topic is crucial for Class 11 Biology and NEET exams.
This Story also Contains
- What are Blood Groups?
- History of Blood Group Discovery
- ABO Blood Group System
- Rh Blood Group System
- Antigens and Antibodies
- Diagnostic Testing for Blood Groups
- Blood Groups NEET MCQs (With Answers & Explanations)
- Recommended Video on Blood Groups
What are Blood Groups?
The term blood type or blood group refers to the division of blood based on the absence or presence of antibodies and hereditary antigenic substances on the surface of RBCs.
Based on the blood group system, these antigens may be proteins, carbohydrates, glycoproteins, or glycolipids. Many additional cell types seen in other organs also have some of these antigens on their surfaces. These red blood cell surface antigens that make up a blood group system can all originate from the same allele (or different gene).
The two most important blood group coding schemes are ABO and Rh, they specify a person's blood type for compatibility with blood transfusions.
History of Blood Group Discovery
In 1901, Karl Landsteiner discovered the AB blood type. He found in 1900 that when red blood cells and serum from a different person are combined in a test tube, the red blood cells agglutinate.
The blood groups A, AB, B, and O were discovered and given names in 1909. In 1930, he was awarded the Nobel Prize. There are three different blood groups, A, B and O, according to the AB blood group, based on whether antigens A, B and O are present or not.
Diagram of Types of blood groups
ABO Blood Group System
The ABO system classifies blood into four types: A, B, AB, and O, according to the kind of antigens found on the cells. The ABO blood group system is one of the most important blood type systems in human biology, identified by Karl Landsteiner in 1901.
Basics of ABO Groups
Antigens: proteins on the surface of RBCs that determine blood type.
Antibodies: Proteins in plasma reacting against the foreign antigens.
Blood types: A (A antigen), B (B antigen), AB, and O (no A or B antigens).
Immune Reactions Between Antigens and Antibodies
Antigens A and B establish blood type based on the presence or absence of specific antibodies.
Agglutination is the clumping of red blood cells when there is a mixing of incompatible blood types, aggregating dangerous reactions.
Genetics of ABO Blood Groups
Inheritance patterns are Mendelian, A and B are dominant, and O is recessive.
The genotypes AA or AO give type A, BB or BO gives type B, AB gives type AB, and OO gives type O.
Types of ABO Blood Groups
Blood Groups | Percent in Population | Features |
O-positive | 35% | Both O-positive and O-negative blood donors can donate blood to individuals with O-positive blood. |
O-negative | 13% | Anyone can receive red blood from an O-negative. This type of donor is referred to as a "universal donor." |
A-positive | 30% | It is the second most prevalent blood type after O-positive. People with A-positive blood and AB-positive blood can receive A-positive red blood cells. |
A-negative | 8% | Only 8% of donors have blood that is A-negative. Comparatively, 30% of donors have blood that is A-positive. |
B-positive | 10% | It is one of the least prevalent blood groups. People with B-positive blood and B-positive blood can receive B-positive red blood cells. |
B-negative | 2% | Red blood cells from B-negative donors are available for about 1 in 8 patients. |
AB-positive | 2% | One of the rarest blood types in the nation, AB-positive blood is only present in 2% of donors. Only individuals with AB + blood can be treated with red blood cells. |
AB-negative | 1% | Only 1% of our blood donors are AB-negative, the rarest blood type in the ABO blood group. |
Diagram showing Genetics of Blood Group Inheritance
ABO Blood Group Compatibility
Blood transfusions: The knowledge of the blood groups to avoid an immune response.
Organ transplant: Donor–recipient matching of their blood group to avoid organ rejection.
Diagram of ABO Blood Group Compatibility
ABO Blood Group Distribution
While Type O is the most frequent in populations all over the world, frequencies of other blood groups vary in different regions.
Differences are prominent in populations and ethnic groups.
Rh Blood Group System
The Rh system determines whether the blood is positive if the Rh factor protein is present, or negative if it is absent. Another critical factor in blood grouping, introduced by Landsteiner and Wiener in 1940.
Diagram of Rh Blood Group System
Basics of Rh Factor
Rh factor: D antigen is a protein present (+) or absent (-) on some RBCs.
Rh-positive: Presence of D antigen.
Rh-negative: Absence of D antigen.
Genetics of Rh Blood Groups
Inheritance of the D antigen is dominant.
DD or Dd is Rh positive and dd is Rh negative.
Clinical Significance
Blood transfusions: Importance of Rh compatibility.
Hemolytic disease of the newborn: This is a condition whereby an Rh-negative woman is carrying an Rh-positive fetus.
Prevention: Rh immunoglobulin therapy for Rh-negative mothers.
Rh Blood Group Distribution
Global distribution More or less 85% of the population is Rh-positive, though different in various ethnic groups and geographical areas.
High incubation of Rh-negative persons in some populations, like Caucasians.
Antigens and Antibodies
Immunogens, also known as antigens, are toxins or compounds in your blood that cause your body to fight them. Immunoglobulins, or Ig, are another name for antibodies. They are Y-shaped proteins produced by B lymphocytes or B cells in your immune system.
What is an Antigen?
Antigens can be various substances from outside your body that provide a health risk. However, they are typically bacteria or viruses. The immune response is the name given to this conflict. Our body's lymphocytes, or disease-fighting white blood cells, are activated in the presence of antigens. Due to the presence of antigens, white blood cells produce immune system defenses termed antibodies.
Types of Antigen
Autoantigens and hetero antigens are the two main types of antigens:
Hetero Antigens are substances made by or found in bacteria, viruses, protozoa, other people's blood and red blood cells, snake venom, allergens like pollen, and certain proteins in food. They are compounds that are foreign to your body.
Our body produces autoantigens, also known as self-antigens, to fight your cells, and they are typically a symptom of a disease such as an autoimmune ailment.
What is an Antibody?
Viruses and other toxins from the outside are attacked and removed by B cells. Making particular antibodies for a specific sort of antigen allows them to achieve this.
These specialised antibodies bind to and mark their unique antigens for the attack. Additionally, antibodies block these antigens, preventing them from damaging your healthy cells.
Types of Antibodies
Immunoglobulins, or antibodies, come in several main categories:
IgG: These are the antibody subtypes that are most prevalent in plasma. They purify dangerous drugs and offer ongoing security.
IgM: The B cells' initial antibodies produced in response to antigens are these.
IgA: Antigens are gathered by these antibodies and eliminated from the body through mucus or other bodily fluids.
IgE: These antibodies elicit allergies and offer parasite defence. Your skin, lungs, and mucosal membranes all contain trace quantities.
IgD: By attaching to B cells, these antibodies trigger the release of IgM antibodies.
Diagnostic Testing for Blood Groups
The typing of blood groups requires precision in many aspects linked to medical procedures.
Sliding Test
One of the simplest and fastest methods in which only drops of blood and several antibody solutions drop onto the surface of a slide are required.
Tube Test
It is more accurate, mixing blood with antibodies in a test tube.
Gel Card Test
This is a more accurate and clear blood typing system using gel matrices.
Molecular Techniques
PCR-based assays for accurate genetic determination of blood type
Blood Groups NEET MCQs (With Answers & Explanations)
Important questions asked in NEET from Blood Group System are:
Antigen-antibody reactions
Genetic inheritance (codominance and multiple alleles)
Blood transfusion compatibility (donors and acceptors)
Practice Questions for NEET
Q1. If no antigen is present on the RBC membrane, the blood group is
A
AB
O
B
Correct answer: 3) O
Explanation:
If there is no antigen present on the RBC membrane, the blood group is O. That is why the O blood group is the universal donor.
Hence, the correct answer is the option 3) O.
Q2. Which of the following blood groups is called a universal donor?
A
O
AB
B
Correct answer: 2) O
Explanation:
Individuals with blood group O can donate blood to individuals with A, B and AB blood groups. Hence, blood group O is called the universal donor
Hence, the correct answer is option 2) O.
Q3. The most popularly known blood grouping is the ABO grouping. It is named ABO and not ABC, because "O" in it refers to having:
Overdominance of this type on the genes for A and B types
One antibody only - either anti-A or anti-B on the RBCs
No antigens A and B on RBCs
Other antigens besides A and B on RBCs
Correct answer: 3) No antigens A and B on RBCs
Explanation:
The "O" in the ABO blood group system signifies the absence of A and B antigens on the surface of red blood cells. In this system, Type A blood has A antigens, Type B blood has B antigens, and Type AB blood has both A and B antigens. Type O blood, on the other hand, lacks both A and B antigens. The designation "O" reflects this lack of antigens, while the plasma of Type O blood contains both anti-A and anti-B antibodies.
Hence, the correct answer is option 3) No antigens A and B on RBCs.
Also Read:
Recommended Video on Blood Groups
Frequently Asked Questions (FAQs)
It is done because different blood types react when combined with certain specific antibodies. This implies that blood typing is very important in transfusions and transplants to ensure that there is compatibility.
If one were given some wrong blood group, that would have led to serious immune responses, agglutination, and hemolysis, serious and at times fatal.
Rh incompatibility may result in hemolytic disease in the newborn. In fact, until recently, Rh incompatibility between mother and fetus caused such diseases that were invariably prevented by Rh immunoglobulin therapy.
The ABO blood group system distinguishes between A and B antigens, while that for Rh is based on the absence of the D antigen.