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Blood Types Explained

Blood Types Explained

Over 6 billion people across the world are placed into a handful of blood group types in order to make various medical procedures simpler. The explanation provided here will enable the reader to understand the composition and the significance of the different blood groups.
Rahul Thadani
Last Updated: Jun 3, 2018
Each individual's blood is made up of four major components; red blood cells, white blood cells, plasma and platelets. The red blood cells (RBCs) transport oxygen to other body cells, white blood cells (WBC) maintain and uphold the body's defense mechanisms, platelets aim to help the process of blood clotting and plasma is where the protein of the body resides.
The blood type (or the group) that a person belongs to, is determined by the red blood cells of the body. Antigens are tiny markers that are present on the surface of these red blood cells, and these antigens are unique for every individual. These antigens help medical professionals determine a person's blood group and during blood transfusions, these antigens need to be matched correctly. Failure to do so, can result in a lot of complications during the blood transfusion process.
The ABO System
The ABO method is the system that is used to determine a person's blood type; a person who has A antigens or B antigens covering the blood cells, will belong to group A or B respectively. And similarly, a person who has none of the antigens will belong to group O and a person with both the antigens will belong to the AB group. The inheritance of blood types from parents is the primary factor in the determination of an individuals blood group, and the International Society of Blood Transfusion (ISBT) recognizes around 30 systems.

The importance of the antigens comes into play during the process of blood transfusion. People with type A blood group will also have antibodies against type B antigens, and vice versa. These two antigens cannot co-exist if their respective anti-bodies are present in the human body. Type O blood group has antibodies against A antigens as well as B antigens and type AB blood group has no antibodies at all.
The Rh System
There is another system in place that helps in describing a person's blood type. This is known as the Rh blood system. This system is primarily based on five Rhesus antigens - C, c, D, E and e, and helps place people in two different blood types (Rh positive and Rh negative). D antigen is the most important of these as it is very likely to cause an immune reaction. If you hear a medical professional mention the term Rh factor, he is referring to the D antigen. The presence of this D antigen on the surface of your blood cells means you are Rh+ (positive), and its absence implies that you are Rh- (negative). These two blood describing systems are used simultaneously to describe a person's blood type. For example, if an individual has blood type O- (O negative), this means that the person does not have A antigens, B antigens and D antigens on his blood cells. A person with a negative blood type cannot receive blood of the positive type and the opposite also holds true.
The blood types explained in the following table shows an estimate by the ISBT about the breakup of different types of blood groups and gives the blood types percentage in the world's population. Majority of the people around the world have type O positive blood.
Blood Type and Rh Factor Percentage of People
A + 34%
A - 6%
B + 8%
B - 1%
AB + 3%
AB - 1%
O + 40%
O - 7%
Importance of Blood Types
The significance of blood groups comes into play during the process of blood transfusion. Once we understand the different blood types, this fact becomes clear. If an incompatible blood type is transfused in your body, it might prove to be fatal. There are a few combinations of blood groups that must not be transfused into a human body at any cost whatsoever. Knowledge of blood groups also helps you prevent blood disorders. The following table will make this clear and also show us different blood donor types. You need to look at the rows of the table and locate your blood group, and then the subsequent boxes of that row will show you which blood groups can donate blood to you without any adverse side effects. You can also locate your blood group by looking at the columns of the table and then determine which blood groups you are permitted to donate to.
Compatible With
Blood Type O- O+ B- B+ A- A+ AB- AB+
AB+ YES YES YES YES YES YES YES YES
AB- YES NO YES NO YES NO YES NO
A+ YES YES NO NO YES YES NO NO
A- YES NO NO NO YES NO NO NO
B+ YES YES YES YES NO NO NO NO
B- YES NO YES NO NO NO NO NO
O+ YES YES NO NO NO NO NO NO
O- YES NO NO NO NO NO NO NO
From the table you can make the following observations.
  • People with type AB+ can receive blood from any person, as their group is compatible with every other blood group.
  • People with type O- can receive blood from no other group except their own.
  • Conversely, AB+ can only donate blood to another person with AB+ group.
  • Lastly, people with O- blood group are universal donors and can have their blood transfused into a person with any group.
Rare blood types can cause a lot of problems for blood banks and hospitals during an emergency. Even geographical locations and atmospheric conditions play an important role in deciding a person's blood group and as a result, certain ethnic groups will have the same blood type in almost all cases.