Healthy people donate a small amount of their blood to be used for blood transfusions. People usually give 1 pint (about 450 milliliters, approximately less than 1/10th of the total amount of blood in the body). Often different components of the blood (see Blood Products) are separated and given to different people.
The entire process of donating whole blood (that is, blood with all component cells) takes about 1 hour. Blood donors must be at least 17 years old (16 in some places with consent of a parent or guardian) and weigh at least 110 pounds (50 kilograms). In addition, they must be in good health. Their pulse, blood pressure, and temperature are measured, and a blood sample is tested to check for low blood count (anemia). Donors are asked a series of questions about their health, factors that might affect their health, and countries they have visited. Certain conditions and factors can permanently or temporarily disqualify people from donating blood. Disqualifying factors typically are those that might make donation dangerous for the donor or risk transmitting a disorder to the recipient. The decision to accept or disqualify a donor can be complicated. The American Red Cross provides detailed information on their web site (see Blood Donation Eligibility Requirements).
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Generally, donors are not allowed to give blood more than once every 56 days. The practice of paying donors for blood has almost disappeared because it encouraged needy people to present themselves as donors and then sometimes to deny having any conditions that would disqualify them.
A person who is deemed eligible to donate blood sits in a reclining chair or lies on a cot. A health care professional examines the inside surface of the person's elbow and determines which vein to use. After the area immediately surrounding the vein is cleaned thoroughly, a needle is inserted into the vein and temporarily secured with a sterile covering. A stinging sensation is usually felt when the needle is first inserted, but otherwise the procedure is painless. Blood moves through the needle and into a collecting bag. The actual collection of blood takes only about 10 minutes, but the whole process from health history to a brief recovery period takes about an hour.
Freshly collected blood is sealed in plastic bags containing preservatives and an anticlotting compound. A small sample from each donation is tested for some infectious organisms.
Testing Donated Blood for Infections
Blood transfusions can transmit infectious organisms carried in the donor's blood. That is why health officials have restricted blood donor eligibility and made blood testing thorough. All blood donations are tested for infection with the organisms that cause viral hepatitis, AIDS, selected other infectious disorders (such as West Nile virus) and syphilis). Sometimes blood is tested for other infections (such as babesiosis and Chagas disease).
Acquired immunodeficiency syndrome (AIDS)
In the United States, donated blood is tested for the human immunodeficiency virus (HIV), the cause of AIDS. The test is not 100% accurate because it will not be positive during the first few weeks after a person has acquired HIV infection. However, potential donors are interviewed as part of the screening process. Interviewers ask about risk factors for AIDS—for instance, whether the potential donors or their sex partners have injected drugs or have other risk factors (see table Some Conditions That Disqualify People From Donating Blood). Because of the blood test and the screening interview, the risk of contracting HIV infection through a blood transfusion in the United States is extremely low—approximately 1 in 1,500,000 to 2,000,000.
Viral hepatitis
Donated blood is tested for infection with the viruses that cause the types of viral hepatitis (types B and C) that are transmitted by blood transfusions.
These tests cannot identify all cases of infected blood, but with the rigorous testing and donor screening procedures, a transfusion poses almost no risk of transmitting hepatitis C. The current risk is less than 1 infection for every 2,000,000 units of blood transfused in the United States.
Hepatitis B remains the most common potentially serious disorder transmitted by blood transfusions, with a current risk of about 1 infection for every 1,000,000 units of blood transfused in the United States.
Syphilis
Blood transfusions rarely transmit syphilis. Not only are blood donors screened and donations tested for the organism that causes syphilis, but the donated blood is also refrigerated at low temperatures, which kills the infectious organisms.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
AABB: Association for the Advancement of Blood and Biotherapies: Information for Donors and Patients: Provides information for patients and blood donors about blood donation safety and procedures and answers frequently asked questions
American Red Cross Eligibility Criteria: Provides information regarding eligibility to donate blood and blood products
