What ABO type is considered the universal donor?

The ABO type considered the universal donor is O negative. This blood type can be safely transfused to patients of all ABO blood groups because it contains no A or B antigens on the surface of its red blood cells. In a blood transfusion, if the recipient's immune system recognizes antigens that are not compatible with its blood type, it can trigger a potentially dangerous immune response. Since O negative red blood cells lack these antigens, they are less likely to be recognized as foreign by the immune system of the recipient, making O negative blood universally acceptable.

While AB negative is often referred to as the universal recipient because individuals with this blood type can receive red blood cells from any ABO group without experiencing an immune reaction, it cannot serve as a universal donor due to the presence of A and B antigens that could be problematic for patients with other blood types. Other options mentioned, such as A negative and B negative, also contain specific antigens that would limit their use as universal donors. Therefore, O negative remains the safest choice for universal donation in emergency situations.