Is O+ a Universal Donor?

Medically Reviewed on 1/20/2022
Is O+ a Universal Donor
Although the blood type O+ can donate blood to all positive blood types, it is not a universal donor. Blood type O- is the universal donor

Although the blood type O+ can donate blood to all positive blood types (A+, B+, AB+, and O+), it is not a universal donor. Blood type O- is the universal blood donor, meaning that people with this blood type can donate blood to all other types with a lower risk of causing serious reactions.

What is a blood group?

Blood groups are an important categorization when it comes to many medical decisions. 

The presence or absence of specific antigens on the surface of the red blood cells—and corresponding antibodies in the plasma—determines blood type.

What are antigens?

Antigens are proteins and polysaccharides that reside on the surface of red blood cells. Depending on the blood group system, these antigens could be carbohydrates, glycoproteins, or glycolipids.

The A antigen is found exclusively in the A blood type, whereas the B antigen is found only in the B blood type. Both A and B antigens are present in the AB blood type. Neither A nor B antigen is present in the O blood type.

If blood antigens are unfamiliar to the body, they can cause an immune reaction, which means a mismatch of blood can clump dangerously inside the veins.

What are antibodies?

Antibodies are disease-fighting proteins found in the plasma that are necessary for immunological responses.

Anti-B antibodies are found in people with blood type A, and anti-A antibodies are found in those with blood type B. Antibodies A and B cause an immune response against the opposite antigens respectively, thus making compatibility necessary.

What are the different classifications of blood groups?

The ABO and Rh-positive or Rh-negative blood type classification is used to classify blood groups.

ABO system

A, B, AB, and O are the four blood types in the ABO system, determined by the presence or absence of the antigens A and B on the surface of red blood cells.

  • Type-A: Contains only the A antigen
  • Type-B: Contains only the B antigen
  • Type-AB: Contains both A and B antigens
  • Type-O: Does not contain either A or B antigens. Because there are no antigens present, an individual with an ABO blood type can receive type-O blood.

Rh factor

Blood can be Rh-positive or Rh-negative based on the presence or absence of the rhesus protein on the surface of red blood cells. Rh-positive indicates the presence of the protein, while Rh-negative indicates the absence of the protein.

A separate set of genes determines Rh blood type from the ones that influence the ABO blood type, one inherited from each parent. People with Rh-negative blood will have a strong immune reaction if Rh-positive blood enters their blood. Thus, it is important to identify a person’s blood type before transfusion.

With the Rh factor in mind, each person can be one of the following 8 blood groups:

  1. A RhD positive (A+)
  2. A RhD negative (A-)
  3. B RhD positive (B+)
  4. B RhD negative (B-)
  5. RhD positive (O+)
  6. RhD negative (O-)
  7. AB RhD positive (AB+)
  8. AB RhD negative (AB-)


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How does blood type play a role in pregnancy?

If the mother has RhD-negative blood, but the fetus has RhD-positive blood, it might lead to difficulties if not properly managed.

During delivery, the blood of the mother and the infant may interact. If this happens, the mother’s body may react to the Rh protein as a foreign material and start producing antibodies against it. This can lead to complications, including miscarriage.

What is the compatibility of different blood types?

  • Blood type O- is compatible with all blood groups. A person with blood type O+ can give blood to anybody with blood groups A+, B+, AB+, or O+; however, as a recipient it is only compatible with the O+ blood group.
  • As a donor, the AB+ blood group is only compatible with the AB+ blood group, but as a recipient, it is compatible with all blood groups. 
  • As donors, blood groups A and B are compatible with blood groups A, AB and B, AB, respectively, and as a recipient, it is compatible with blood groups A, O and B, O, respectively.

Why is it important to know your blood type?

You should know your blood group for the following reasons:

  • You may require compatible blood for a blood transfusion after an accident, surgery, or childbirth
  • Knowing which diseases are associated with your blood type can help you take precautionary measures and reduce risk factors.
  • You can help save a person’s life if they require a blood transfusion.

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Medically Reviewed on 1/20/2022
Image Source: iStock Images

Mitra R, Mishra N, Rath GP. Blood groups systems. Indian J Anaesth. 2014;58(5):524-528.

Stanford Blood Center. Blood Types.

The Royal Children's Hospital Melbourne. Blood Groups and Compatibilities.