Blood donors generally give whole blood. In many cases, though, they donate plasma. While some countries transfuse whole blood, more commonly, blood is separated into its primary components before it is tested and used in transfusion medicine. Note the four primary components, their functions and the percentage of total blood volume each represents.
PLASMA: This constitutes between 52 and 62 percent of whole blood cells, proteins, and other substances are suspended and transported.
Water constitutes 91.5 percent of plasma (including albumins, which make up about 4 percent of the plasma: globulins, about 3 percent: and fibrinogen, less than 1 percent). The remaining 1.5 percent of plasma is made up of other substances, such as nutrients, hormones, respiratory gases, electrolytes, vitamins, and nitrogenous wastes.
WHITE BLOOD CELLS : (LEUKOCYTES) This constitute less than one percent of whole blood. These attack and destroy potentially harmful foreign matter.
PLATELETS: (THROMBOCYTES) It constitutes less than one percent of whole blood. These form clots, blocking blood from exiting wounds.
RED BLOOD CELLS: (ERITROCYTES) This constitute between 38 and 48 percent of whole blood. These cells keep tissue alive by bringing oxygen to it and taking carbon dioxide away.