What is ABO Incompatibility?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 01 October 2019
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ABO incompatibility refers to medical reactions that can occur if two different blood types are mixed in the same body, resulting in an immune or inflammatory reaction. There are three scenarios under which this circumstance occurs. The first is when people receive a blood transfusion of an incompatible type of blood, the second is when a newborn and mother have incompatible blood types, and the third scenario occurs when an organ transplant comes from someone who doesn’t share the same blood type. Except in the third case, this illness is typically easily treated if caught early, but serious complications might still occur. Organ transplantation of the wrong blood type can be very challenging.

Human blood is classified into A, B, O, and AB, based on the presence of certain molecules, and these molecules don’t always react well when placed in a body that doesn’t also contain them. The body can begin to react or have an immune response if it receives the wrong type of blood and senses the molecules or antigens. Some different types can be transfused to other people — A, B, and AB blood types may usually receive type O blood, because it doesn’t contain antigens that result in inflammation. Another consideration is the Rh factor, which determines whether blood is negative or positive.


The immune response of ABO incompatibility most affects the liver and it can cause people to develop jaundice. Other symptoms of this illness include presence of blood in the urine, pain in the back, and fever. Some adults note the sensation of great worry when they’ve been given the wrong blood. As the condition progresses, blood pressure could drop sharply, and there is need to get treatment right away, especially after a blood transfusion.

Treatment to address ABO incompatibility must begin soon, and it would include transfusing fluids, and giving medications that could stop reactions to the wrong blood antigens. These medications might be antihistamines, steroids or a combination of the two. The person would be watched carefully to make certain such treatments were working.

In newborns, treatment may be slightly different. To address jaundice, special lights or light blankets can be used to reduce bilirubin levels, and some babies require blood transfusions with the appropriate blood. Usually, babies with ABO incompatibility are not as sick with this condition than adults who receive transfusions, but they still require medical care.

The circumstances under which a person would receive an organ of the wrong blood type or a transfusion are extremely rare. ABO incompatibility is avoided by testing for blood type, and with a blood transfusion or organ transplant, usually the only way it occurs is due to a mistake. Transplant of an incompatible organ is indeed a serious mistake because rejection may occur quickly.

In infants, ABO incompatibility is more difficult to avoid. Couples who have different incompatible blood types may produce children with blood types incompatible to the mother. Knowing the blood types of the parents is useful to gauge risk of this condition occurring.


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