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ABO incompatibility

A, B, AB, and O are the four major blood types. The types are based on small substances (molecules) on the surface of the blood cells.

When people who have one blood type receive blood from someone with a different blood type, it may cause their immune system to react. This is called ABO incompatibility.


The different blood types are:

  • Type A
  • Type B
  • Type AB
  • Type O

People who have one blood type may form proteins (antibodies) that cause their immune system to react against one or more of the other blood types.

Being exposed to another type of blood can cause a reaction. This is important when a patient needs to receive blood (transfusion) or have an organ transplant. The blood types must be compatible to avoid an ABO incompatibility reaction.

For example:

  • A patient with type A blood will react against type B or type AB blood.
  • A patient with type B blood will react against type A or type AB blood.
  • A patient with type O blood will react against type A, type B, or type AB blood.
  • A patient with type AB blood will not react against type A, type B, type AB, or type O blood.

Type O blood does not cause an immune response when it is given to people with type A, type B, or type AB blood. This is why type O blood cells can be given to patients of any blood type. People with type O blood are called universal donors. But people with type O can only receive type O blood.

Both blood and plasma transfusions must be matched to avoid an immune reaction. Before anyone receives blood, both the blood and the person receiving it are tested carefully to avoid a reaction. Usually a reaction occurs because of a clerical error causing a patient to receive incompatible blood.


The following are symptoms of ABO incompatible transfusion reactions:

  • Back pain
  • Blood in urine
  • Chills
  • Feeling of "impending doom"
  • Fever
  • Yellow skin (jaundice)

Exams and Tests

The health care provider will perform a physical exam. Blood tests will usually show:

Urine tests show the presence of hemoglobin due to breakdown of red blood cells.


Treatment may include:

  • Drugs used to treat allergic reactions (antihistamines)
  • Drugs used to treat swelling and allergies (steroids)
  • Fluids given through a vein (intravenously)
  • Medicines to raise blood pressure if it drops too low

Outlook (Prognosis)

ABO incompatibility can be a very serious problem that can result in death. With the right treatment, a full recovery is expected.

Possible Complications

  • Kidney failure
  • Low blood pressure needing intensive care
  • Death

When to Contact a Medical Professional

Call your health care provider if you have recently had a blood transfusion or transplant and you have symptoms of ABO incompatibility.


Careful testing of donor and patient blood types before transfusion or transplant can prevent this problem.


Goodnough L. Transfusion medicine. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine

Update Date 5/29/2014

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