A TO O: BLOOD TYPES, DONATION AND COMPATIBILITY

Medically Reviewed by Dr. Sony Sherpa, (MBBS) - September 30, 2024

Blood plays a crucial role by transporting nutrients and oxygen to our cells and well as eliminating waste. But not all blood is the same. In fact, there are different types of blood, each with its own unique characteristics.

In this article, we will define the different blood types from A to O, explaining what makes each one unique and which types are compatible with blood donation.

What Are Blood Types?

The presence or absence of certain substances on the surface of red blood cells determines the blood type, also known as the blood group. They consist of either sugars or proteins. These compounds are also known as antigens for their ability to trigger an immune reaction.^[1]

There are many blood-type antigens found on the surface of red blood cells. Many of them contribute towards the stability of red blood cell membranes as well as self-tolerance. Self-tolerance is the ability of the immune system to tell if a cell is foreign or not. The blood type antigens of a person are unique to them and register as self-antigens to the immune system.

During a blood transfusion, the blood that is administered needs to contain matching antigens. If it does not, it will trigger an immune response in the recipient due to the presence of antibodies that target foreign blood-type antigens. When a blood type antibody binds to a blood antigen, it causes the blood to clot and can cause a life-threatening blood clotting event (thrombosis), heart attack, or stroke.

Common Blood Types

There are thought to be 22 blood group systems in total that comprise different blood type antigens. The main one is the ABO blood group system, consisting of four main blood types: A, B, AB, and O.^[2]

The presence (or lack) of two antigens, A and B, on the surface of red blood cells determines these blood types.

Type A

Type A is the second most common blood type, with approximately 30% of the population having it.

People with type A blood have the A antigen on the surface of their red blood cells. They also have anti-B antibodies in their plasma, which means their body will attack any B antigens that enter their system.

Type B

Type B is the third most common blood type, found in approximately 10% of people.

People with type B blood have the B antigen on their red blood cells surface, and the plasma contains anti-A antibodies. This means that the bodies of people with type B blood will attack any A antigens that enter their system.

Type AB

Type AB is the rarest blood type, present in only about 4% of the population.

Red blood cells with type AB blood have both A and B antigens on their surface, but the plasma contains no antibodies. People with type AB blood are, therefore, universal recipients since they can receive blood from any blood type. However, they can only donate to other AB individuals.

Type O

Type O is the most common blood type, with approximately 45% of the population having it.

The main characteristic of people with Type O blood is the absence of A and B antigen on the cell surface; but they have both anti-A and anti-B antibodies in the plasma. This means that people with type O blood can donate to any blood type, making them universal donors. However, they can only get blood from other people who are type O.

Rare Blood Types

While the four main blood types are the most common, there are also rare blood types that are found in a small percentage of the population. These rare blood types can make it difficult for the individuals possessing them to find compatible blood donors if they need a blood transfusion.

Rh-Negative Blood

The Rh blood group refers to the presence or absence of the Rh factor on the surface of red blood cells. The Rh factor is an antigen that can cause adverse reactions if it is mismatched during a blood transfusion.^[3]

Rh-negative blood types are rare, with presence in only about 15% of the population. This means most people have Rh-positive blood, where they have the Rh antigen on the surface of their red blood cells. Rh-negative blood types do not have the Rh antigen, which can cause complications during blood transfusions and pregnancy if the mother is Rh-negative and the baby is Rh-positive.

It is important to note that the positive or negative designation of the Rh blood group is independent of the ABO blood type (A, B, AB, or O). This means that someone with blood type A can also have a positive or negative Rh factor, resulting in blood types such as A+, A-, B+, B-, AB+, AB-, O+, or O-.

Bombay Blood Group

The rarest blood type is known as the ‘Bombay blood group." It is more common in India, found in 1 in every 10,000 people. By comparison, only about 1 in a million Europeans have this blood type.

This blood type is also known as the Hh blood group. Hh is the building block antigen for all blood type antigens. Those with the Hh blood type are deficient in Hh and like those with type O blood, lack A and B antigens on the surface of their red blood cells. A person with type O blood also does not display A or B antigens, yet their blood is not deficient in Hh.

Individuals with the Bombay blood group can only receive blood from others of the same blood type.

Blood Compatibility

Blood compatibility refers to the ability of one person's blood to be safely transfused into another person's body without causing an adverse reaction. This is determined by the presence or absence of antigens and antibodies in the blood.^[4]

Compatible Blood Types

Type A blood is compatible with type A and type O blood.

• A positive (+) blood type can receive blood from A positive (+), A negative (-), O positive (+), and O negative (-) blood types.
• A negative (-) blood type can receive blood from A negative (-) and O negative (-) blood types.

Those with type A blood have the A antigen on the surface of red blood cells and anti-B antibodies in the plasma. Type O blood has neither A nor B antigens on the surface of red blood cells, making it safe for type A individuals to receive.

Type B blood is compatible with type B and type O blood.

• B positive (+) blood type can receive blood from B positive (+), B negative (-), O positive (+), and O negative (-) blood types.
• B negative (-) blood type can receive blood from B negative (-) and O negative (-) blood types.

Type B blood is characterized by the presence of anti-A antibodies in the plasma and the B antigen on the surface of red blood cells. Individuals with type B blood can safely receive type O blood since its red blood cells do not contain A or B antigens.

Type AB blood is compatible with all blood types.

• AB positive (+) blood type can receive blood from any blood type.
• AB negative (-) A negative (-), B negative (-), AB negative (-), and O negative (-) blood types can donate blood to AB Negative (-).

This is because red blood cells with type AB blood have both A and B antigens on their surface, and the plasma contains no antibodies. This means that type AB individuals can receive blood from any ABO blood type without experiencing an adverse reaction.

Type O blood is compatible with type O blood.

• O positive (+) blood type can receive blood from O positive (+) and O negative (-) blood types.
• O negative (-) blood type can receive blood from O negative (-) blood type.

This is because type O blood has neither A nor B antigens on the surface of red blood cells and antibodies towards A and B antigens in the plasma.

Incompatible Blood Types

Type A blood is incompatible with type B and AB blood. A negative (-) blood is also incompatible with A positive (+) and O positive (+) blood. This is because type A blood has anti-B antibodies in the plasma, which will attack any B antigens from type B blood that enter the body.

Type B blood is incompatible with type A and AB blood. B negative (-) blood is also incompatible with B positive (+) and O positive (+) blood. This is because type B blood has anti-A antibodies in the plasma, which will attack any A antigens from type A blood that enter the body.

Type AB blood is compatible with all blood types. However, AB negative (-) blood is incompatible with any positive blood type. This is because type AB blood has no antibodies in the plasma, meaning that it won't attack antigens from any blood type donation.

Type O blood is compatible with type O. However, a person with O negative blood type cannot receive blood from an O positive donor. This is because type O blood has both anti-A and anti-B antibodies in the plasma, which will attack any A or B antigens that enter the body.

Blood Donation

The act of willingly donating blood for use in medical procedures or life-saving transfusions is known as blood donation. Blood donations are essential for maintaining an adequate supply of blood for those in need. However, not everyone is able to donate blood.

Eligibility to Donate Blood

To be eligible to donate blood, you must meet certain criteria, including:

• Minimum age should be 17 years (16 with parental consent)
• Weighing at least 110 pounds
• Being in good health
• Not having any infectious diseases
• Not having recently traveled to certain countries
• Not having recently received a tattoo or piercing
• Not having recently donated blood

Types of Blood Donations

Blood type applies to all forms of blood donation except for platelet transfusions, which lack blood group antigens and antibodies.

There are four types of blood donations, each with their pros and cons^[5]:

• Whole blood donation: This is the most common type of blood donation, where a pint of blood is collected from the donor.
• Platelet donation: This type of donation is used to help patients with blood disorders or cancer. Platelets are collected through a process called apheresis, where blood is drawn from one arm, passed through a machine that separates the platelets, and then returned to the donor through the other arm.
• Plasma donation: Important proteins and antibodies are found in the liquid component of blood called plasma. Plasma donations are used to help patients with severe burns, shock, or other conditions. Similar to platelet donation, plasma is collected through apheresis.
• Double red cell donation: This type of donation is similar to whole blood donation, except that two units of red blood cells are collected instead of one. This type of donation is used to help patients with severe anemia or those who need a large amount of blood.

Which Blood Types Should Donate Blood?

When it comes to blood donation, rare blood types are particularly valuable due to being in short supply. Those with type O blood are also encouraged to donate more often, as their blood can be transfused to most recipients without complications.

Conclusion

In conclusion, blood types play a crucial role in determining blood compatibility and who can donate to whom. Understanding the different blood types and their compatibility can help ensure that patients receive the blood they need during a transfusion. If you are eligible, consider donating blood to help save lives and make a difference in your community.

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