Which blood type could be given as a transfusion for patient with AB blood when the RH factor is unknown?

A patient with AB blood can receive blood from any ABO blood type (A, B, AB, or O) because AB individuals have both A and B antigens and can accept all blood types. When the Rh factor is unknown, it is safest to transfuse Rh-negative blood to avoid potential complications. Therefore, O-negative blood would be the best choice, as it is considered the universal donor and is safe for all recipients.