Final answer:
In an emergency situation when the patient's blood type is unknown, it is common to transfuse type O-negative blood, which is considered the universal donor. This blood type lacks the A and B antigens, making it compatible with any blood type. While it is not ideal to transfuse blood without knowing the patient's blood type, in critical situations where time is limited, type O-negative blood can save lives.
Step-by-step explanation:
When you have an unidentified patient in the ER for a blood draw, a common practice is to give the patient type O-negative blood. Type O-negative blood is considered the universal donor because it lacks the A and B antigens on red blood cells. This means that it can be transfused to patients with any blood type without causing an adverse reaction. While it is not ideal to transfuse blood without knowing the patient's blood type, in emergency situations where there is no time to determine the blood type, type O-negative blood can be a life-saving option.