• Red cells: blood cells that transport oxygen to body cells and remove carbon dioxide from the bloodstream.
• White cells (leukocytes): blood cells that protect the bloodstream from bacteria.
• Platelets: blood cells that help control bleeding by helping the clotting process.
• Plasma: consisting of 92 percent water, seven percent protein and one percent minerals, it's the source for gamma globulin, albumin and clotting factors.

Thanks to advances in medical technology, blood can be separated into its different components. Hence, a unit can be broken down into these components, which then can be given to people who have different blood needs.

• Red blood cells are used to treat anemia and blood loss resulting from trauma and surgery. Some heart operations can use up to 20 pints of red cells. Liver transplants normally use 10-20 pints and a hip replacement, 1-3 pints.
• Platelets are commonly used in treating cancers like leukemia. One patient can require the platelets from eight or more individual donations every day for weeks.
• Plasma is used for treating hemophilia, surgical shock, severe burns and immunodeficiency.