Final answer:
A mismatch in blood types can lead to a transfusion reaction, causing clumping of red cells and restricted blood flow. To avoid this, it is crucial to match blood types correctly, but in emergencies, type O blood can be transfused. However, introducing type O blood to a recipient with different blood types can still cause problems due to the introduction of antibodies against A and B antigens.
Step-by-step explanation:
When a donor's blood cells have a carbohydrate (A or B) that is foreign to the recipient, a mismatch occurs and can lead to a transfusion reaction. The red cell antigens of one blood group interact with antibodies in another blood group, causing the red cells to clump and restrict blood flow. This can be life-threatening for the transfusion recipient. To avoid transfusion reactions, it is crucial to match blood types correctly. In emergency situations, when there is no time for cross-matching, type O blood, which lacks A and B antigens, can be transfused as it is considered the universal donor. However, introducing type O blood into a recipient with type A, B, or AB blood may still cause some problems due to the introduction of antibodies against A and B antigens. Therefore, it is always preferable to cross-match a patient's blood before transfusing if possible.