ABO

Blood types A, B, O

The ABO blood group system classifies human blood into four main types based on the presence or absence of antigens on the surface of red blood cells:

• Type A: Has A antigens on red blood cells and anti-B antibodies in the plasma.
• Type B: Has B antigens on red blood cells and anti-A antibodies in the plasma.
• Type AB: Has both A and B antigens, with no anti-A or anti-B antibodies, making it the universal recipient.
• Type O: Has no A or B antigens but both anti-A and anti-B antibodies, making it the universal donor for red blood cells.

Mismatched blood types is referred to as ABO incompatibility. This system is critical for safe blood transfusions and organ transplants, as incompatible blood types can trigger severe immune reactions.