As the baby blood cells mature, they develop into one of several different types. Red cells contain hemoglobin, a pigment which carries oxygen to the tissues of the body. Platelets are the special cells that clump together and control bleeding after an injury. Blood cells are carried through the circulatory system in watery fluid called plasma. Donated blood is collected in specialized centers called blood banks.
Platelets have the shortest shelf-life and can be stored for only about five days.
Red cells can be stored for up to 42 days. Plasma can be frozen and stored for up to one year. The Blood Supply Nationwide, about 32,000 units of blood are needed every day. But adequate supplies of blood aren t always available. Researchers say those shortages may reflect a growing trend.