An individual whose blood type is B may in an emergency donate blood to a person whose blood type is :

Blood group compatibility is determined by the presence of antigens on red blood cells and antibodies in the plasma. An individual with blood type B has B antigens on their red blood cells and anti-A antibodies in their plasma [t5]. In a transfusion, a donor's red blood cells must not be attacked by the recipient's antibodies. Type B individuals can safely donate to recipients of the same blood type (B) because they share the same antigen profile [t1][t7]. Additionally, they can donate to individuals with blood type AB. Type AB individuals are known as 'universal recipients' because they lack both anti-A and anti-B antibodies, allowing them to receive blood from any ABO group without an immune reaction [t1][t3][t8]. Therefore, in an emergency, a type B donor can provide blood to persons with type B or AB blood [t1][t5].