When should hospitals prefer O positive over O negative?

Hospitals prefer to use O positive (O+) blood whenever it is safe to do so, primarily to conserve the extremely limited supply of O negative blood. O+ is the most common blood type (about 38% of people), making it more available.

Here is when O+ is preferred over O-:

1. For Rh-Positive Patients: The vast majority of the population (about 85%) is Rh-positive. Any patient with an Rh-positive blood type (A+, B+, AB+, or O+) can safely receive O positive blood. Using O+ for these patients is the standard, most efficient practice.
2. Routine Transfusions for O+ Patients: For a patient who is known to be O positive and needs a transfusion, O+ is the first choice.
3. In Some Emergencies (for men): If a male patient's blood type is unknown in an emergency, some trauma centers may use O positive blood to save the O negative supply, as there is no risk of future pregnancy complications (like hemolytic disease of the newborn).

In short, O negative is reserved for two critical cases: emergencies where the patient's type is unknown (especially for females of childbearing age) and for all patients who are Rh-negative (A-, B-, AB-, O-).