What happens when they do not match for blood groups?

Blood groups are determined by the presence or absence of specific antigens on the surface of red blood cells. When a patient receives a blood transfusion, the donor's red blood cells must be compatible with the patient's plasma in order to avoid a transfusion reaction. If the donor's red blood cells have antigens that the patient's plasma does not recognize, the patient's immune system will attack and destroy the donor's red blood cells, causing a transfusion reaction.

Transfusion reactions can range in severity from mild to life-threatening. Mild transfusion reactions may cause fever, chills, and hives. More severe transfusion reactions can cause difficulty breathing, low blood pressure, and kidney failure. In rare cases, transfusion reactions can be fatal.

To avoid transfusion reactions, blood banks carefully screen donor blood to make sure that it is compatible with the recipient's blood. Blood is tested for ABO blood group, Rh factor, and other antigens. If the donor's blood is not compatible with the recipient's blood, the transfusion will not be performed.

In some cases, a patient may need to receive a blood transfusion from a donor who has a different blood group. This is called an incompatible blood transfusion. Incompatible blood transfusions are more likely to cause a transfusion reaction than compatible blood transfusions, but they may be necessary in order to save the patient's life.