Every year approximately 4.5 million people receive blood transfusions in the United States. This life saving blood is donated by about 8 million volunteers according to the National Blood Data Resource Center. Many people are repeat donors. The World Health Organization reports that the need for blood is increasing by 1% every year globally while the amount donated is decreasing by 1% annually. This will inevitably result in serious blood shortages in the near future. It is hoped that this shortfall will be alleviated by the invention of better methods of blood preservation and effective synthetic blood.
It is generally safe to donate whole blood once every two months or plasma more often. However, not everyone who wishes to give blood is accepted. Potential donors in the U.S. must be healthy, at least 17 years old, and weigh 110 pounds or more. In addition, they are screened for a range of contagious diseases and risky behavior that is associated with them in order to assure the safety of the blood supply. Donated blood is routinely tested for hepatitis B and C, HIV-1 and 2, syphilis, and some strains of human T-lymphotrophic virus. Donors are commonly rejected if they have engaged in homosexual sex, are prostitutes, have injected certain illegal drugs, had certain diseases (e.g., cancer, chagas, or babesiosis), or recently been in countries that have diseases transmitted via blood (e.g., malaria or variant Cruetzfeldt-Jakob disease--commonly called mad-cow disease). In addition, recent use of aspirin and a number of other medications that can affect blood components may be reason for exclusion.
Usually only one unit (about a pint) of blood is drawn from a donor's arm during a donation. The blood is typically separated into four key components--red cells, platelets, cryoprecipatiated AHF (antihemphilic factor), and plasma. Blood transfusions in hospitals today generally only contain plasma and red cells. This allows the same unit of blood to be used by more people since not everyone needing blood require all of its parts. Men usually have about 12 pints of blood in their bodies and women have about 9. The fluid lost from a donation of 1 unit of blood is normally replaced in 24 hours, however, it takes several weeks for bone marrow to produce enough red cells to replace those that are lost.
Whole blood is usually stored for no more than 42 days. Recent clinical studies reported by Timothy McMahon at Duke University, suggest that stored blood begins to lose its effectiveness in as little as 2 weeks. Apparently, the red cells do not take up oxygen as readily. They also become less flexible, which makes it more difficult for them to pass through the narrowest capillaries.
For more information about blood donation go to the website of the American Association of Blood Banks.
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