Final answer:
In situations requiring immediate blood transfusions without known blood types, type O blood is used as it's the universal donor. Scheduled transfusions involve determining the patient's ABO blood type through cross matching to prevent hemolytic transfusion reactions.
Step-by-step explanation:
Blood transfusions are a critical part of medical procedures, such as surgeries, where blood loss is expected. It is essential to match the ABO blood type of the donor with that of the recipient to prevent a hemolytic transfusion reaction (HTR), which can be life-threatening. In emergency situations where there's no time to determine the patient's blood type, type O blood is often used because it is considered the universal donor for red blood cells and has the highest likelihood of being accepted without causing an adverse reaction.
For the case described, if a patient, like David Jones, requires a transfusion and the blood type cannot be determined in time, or family members don't know their blood types, type O blood might be transfused. In pre-scheduled procedures, a patient's blood type is determined through cross matching, which involves testing the blood against specific antibodies. If both anti-A and anti-B antibodies cause agglutination, the blood type is AB, indicating the presence of both type A and B antigens on the red blood cells.