Home Health A-Z Who is a Universal Donor? Know all the Other Blood Groups Too

Who is a Universal Donor? Know all the Other Blood Groups Too

Verified By Dr Amitav Mohanty February 8, 2021 308587 0
Universal Donor
Universal Donor

What Is a Universal Blood Donor?

A universal donor is a person who can donate blood to any recipient of any blood group. 

In some emergencies, donors with the same blood group as the patient may not be available. In such cases, a person with group O, specifically O negative, can donate blood to the patient. This blood group barely causes any reactions to the recipient and is called a universal donor blood group.

More About a Universal Blood Donor

Although people with an O blood type are commonly known as universal blood donors, people with O- (negative) blood type are the true universal donors. It is because their red blood cells do not carry antigens. So, they can donate blood to any other blood group. A person with blood group O+ (positive cells) cannot give blood to an Rh-negative individual.

The blood group type O (positive and negative) is in high demand due to its need during emergencies. However, about 7% of people have an O-negative blood type, and about 37% of the population has an O-positive blood type, making it a common blood group.

How is the Blood type determined?

Blood groups are determined by the presence and absence of antigens in the blood. The antigen helps trigger the immune system if any foreign body enters the bloodstream and produces antibodies to fight it.

The blood contains red blood cells, white blood cells, and platelets in plasma – a liquid in the blood. The presence of antigens A&B on the surface of RBCs decides the four main blood groups. Besides this, the presence or absence of the Rh factor, a protein, determines if your blood group would be negative or positive. Depending on these factors, the blood type can be A+, A-, B+, B-, O+, O-, AB+ or AB-. The International Society of Blood Transfusion (ISBT) recognizes  38 human blood group systems. Among these 38 systems, the ABO and Rh are the most widely used. It is vital to know a person’s blood type in case of emergencies or if there is a need for a blood transfusion.

Which Blood Group Types Are Universal Donors?

The blood type or the blood group is a form of classification of blood that depends on the presence and absence of antibodies and inherited antigens on the surface of red blood cells.

Our blood contains red blood cells, white blood cells, and platelets in a liquid called plasma. 

Antigens are molecules found on the surfaces of the red blood cells and contain protein and carbohydrates. Antibodies are protein molecules called Immunoglobulins (Ig) found in plasma. Antibodies bind specifically to the corresponding antigen on the red blood cells. Antibodies are our natural defense mechanisms and are produced by the immune system when there is exposure to a foreign antigen.

Simply put, the people with type O negative blood are universal red cell donors, and people with type AB blood group are universal plasma donors.

Why Do You Need to Know Your Blood Type?

It is crucial to ensure that the blood type of the donor and recipient are matching when it comes to blood transfusions. Some antigens can make your immune system consider the transfused blood as a foreign body and attack it. Therefore, cross-matching and correct blood-typing are critical.

ABO Blood Group System

The ABO blood group system defines four main blood groups. It includes Type A, B, AB, and O.

Antigens and Antibodies play a crucial role in determining a person’s blood type.

Blood GroupAntigens (in red blood cells)Antibodies (in plasma)
OnilAnti-A, Anti-B
ABA, Bnil

Hence, during blood transfusions, an agglutination reaction occurs between similar antigen and antibody. Agglutination means the clumping of particles. If the antigen and antibodies are not similar, the antibody will attack the antigen as a defensive action by the immune system.

This also explains why O type is a universal donor since it has no antigens present in the first place to be attacked by antibodies. Similarly, AB type is a universal recipient since it does not have any antibodies present in order to attack antigens.

Rh System

Apart from the ABO system, there is another system to determine a person’s blood group. It is known as the Rh system. Rh, meaning Rhesus system, contains 49 blood group antigens, out of which five are most significant. The most significant Rh antigen is the D antigen because it is the most likely to provoke an immune system response of the five main Rh antigens. If present, the blood group is called RhD+ (positive), and if absent, it is RhD- (negative).

As mentioned earlier, the O- blood type can be safely given to any person with any blood type since it does not contain any A, B, or RhD antigens on the surface of the red blood cells. Hence, it is compatible with every other blood group of the ABO and Rh system.

What Are Blood Types and Transfusion?

The Donor/Recipient concept goes as follows:

  • Type A. The person can receive blood only from Type A and O and can donate to individuals with Type A and AB.
  • Type B. The person can receive blood only from Type B and O and can donate to individuals with Type B and AB.
  • Type O. The person can receive blood only from Type O but can donate to any of A, B, and AB.
  • Type AB. The person can receive blood from any type but can only donate to AB type.

Blood Transfusion

Blood transfusion is a way of infusing blood into the body after an illness or injury. Some of the many cases where you may need blood transfusions are:

  • Expecting mothers with labor complications
  • Severe accident
  • Premature babies
  • Cancer treatment

Blood transfusion is of several kinds:

What Is the Process to Check One’s Blood Group?

To determine your blood group, a lab technician will mix your blood sample with antibodies that attack types A and B blood to see how it reacts. Then, they will check it to see if agglutination (clumping) is taking place or not. 

For example, your blood type is B, and the technician mixed the sample with an anti-Rh serum. 

If your blood cells clump together in response to the anti-Rh serum, it means that you have Rh-positive blood.  

If the blood sample does not react to Anti-A or Anti-B antibodies, it is blood group O.

There are certain myths that have resulted in people having misconceptions about the entire blood group concept. It’s time that we debunk them one by one.

  • Blood Type does not determine your personality type. In Japan, each blood type is associated with a personality type. While it sounds interesting, there is no relation whatsoever.
  • Mosquitoes do not have a preference for O blood type. It is often said that people with O type attract mosquitoes, but there is no such relation between the two. Mosquitoes are drawn by the carbon dioxide and heat majorly.
  • No blood type is more prone to illness over the other. Blood type has little to no effect on body health.
  • There is no blood type that isn’t needed. Every blood type is needed, and every blood type can make a difference.

Importance of Blood Donation

  • A single donation can save three lives. One blood donation provides components that can help upto three different people.
  • Donations are the only way of giving blood to someone who needs it. Blood is not manufactured in a laboratory despite numerous advancements in technology.
  • Before donation, the donor undergoes a simple physical examination and blood test that will check his/her blood pressure, body temperature, heart rate, and hemoglobin levels.
  • Contributing to the community is a vital service, and making a difference in someone’s life can boost one’s sense of well-being.


It is crucial to have a proper classification of blood groups for blood transfusion. If the blood samples of two different blood groups are mixed, the blood will clump because the antibodies of the recipient’s blood will naturally fight the cells resulting in a toxic reaction.

Frequently Asked Questions

Why is O + a universal donor? 

Although O+ is considered to be a universal donor, O- is the actual universal donor because A, B, and Rh antigens are absent in the latter. So, it can be given to anyone, irrespective of the blood group.

Which blood type is rarest?

The rarest blood type is AB negative.

Why is O negative so rare?

Compared to other blood types, O-negative is the most commonly required blood type in hospitals because people with O-negative blood type are universal donors.

What blood type can reject pregnancy?

If the Rh factor of the expectant mother and her unborn child are different, it is known as Rh incompatibility. It usually happens when the mother is -ve, and the baby is +ve.



Verified By Dr Amitav Mohanty
MBBS, MD -Medicine, Senior Consultant - General Medicine, Apollo Hospitals Bhubanswar

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