Final answer:
In an emergency with no time for blood typing, type O blood is transfused to prevent a hemolytic transfusion reaction. For planned procedures, a patient's blood type is identified by testing for agglutination with anti-A and anti-B antibodies; visible agglutination in both indicates blood type AB.
Step-by-step explanation:
In emergency situations where a patient's blood type cannot be determined swiftly, such as in the case of severe traumatic injuries with critical bleeding following a motor vehicle accident, the type of blood transfused is O blood, often known as the universal donor type. The reason for using type O blood is to prevent a potentially fatal reaction known as a hemolytic transfusion reaction (HTR), which occurs if the patient receives incompatible ABO blood type. Additionally, an antibody screening test is conducted to ensure the patient is not making antibodies against antigens outside the ABO or Rh systems.
For a scheduled surgery, a patient's blood type is determined by adding anti-A and anti-B antibodies to samples of their blood. If both samples are visibly agglutinate, this is a normal response for blood type AB, indicating that the patient has both A and B antigens present on their red blood cells. There is no technician error in this type of determination process.