The main types of blood are A, B, AB, and O.
Transfusions of blood are possible only when the blood types are compatible. If
the blood types are not compatible proteins in the plasma will recognize foreign
antigens on red blood cells and respond by causing the cells to agglutinate, or
clump, a condition that causes blockage in small blood vessels and often death.
The following table summarizes the blood proteins involved in blood types.
Proteins of Blood Types
Blood Cell Plasma
Type Antigen Antibody
A A b
B B a
AB AB none
O none a and b
Note: Type AB -- universal recipient
Type O -- universal donor
