Healthy people donate a small amount of their blood to be used for blood transfusions Overview of Blood Transfusion A blood transfusion is the transfer of blood or a blood component from one healthy person (a donor) to a sick person (a recipient). Transfusions are given to increase the blood's ability to... read more . People usually give 1 pint (about 450 milliliters, approximately less than 1/10th of the total amount of blood in the body) and often different components of the blood (see Blood Products Blood Products People are sometimes given transfusions of whole blood during severe bleeding (for example after an injury or pregnancy complications), but usually they are given only the blood component they... read more ) 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 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 Overview of Anemia Anemia is a condition in which the number of red blood cells is low. Red blood cells contain hemoglobin, a protein that enables them to carry oxygen from the lungs and deliver it to all parts... read more ). 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).
Did You Know...
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 worker 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.
The standard unit of donated blood is about 1 pint (about 450 milliliters). 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 viral disorders (such as Zika virus Zika Virus Infection Zika virus infection is a mosquito-borne viral infection that typically causes no symptoms but can cause fever, rash, joint pain, or infection of the membrane that covers the white of the eye... read more and West Nile virus), Chagas disease Chagas Disease Chagas disease is an infection caused by the protozoan Trypanosoma cruzi, which is transmitted by the bite of a kissing bug (also called an assassin or Triatominae bug). The protozoa may enter... read more , and syphilis Syphilis Syphilis is a sexually transmitted disease caused by the bacteria Treponema pallidum. Syphilis can occur in three stages of symptoms, separated by periods of apparent good health. It begins... read more .
Acquired immunodeficiency syndrome (AIDS)
In the United States, donated blood is tested for the human immunodeficiency virus Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and can cause acquired immunodeficiency syndrome (AIDS). HIV is transmitted... read more (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 had sex with a man who has male sex partners. 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—1 in 1,500,000 to 2,000,000 according to recent estimates.
Donated blood is tested for infection with the viruses that cause the types of viral hepatitis The Hepatitis Viruses Hepatitis is inflammation of the liver. (See also Overview of Acute Viral Hepatitis and Overview of Chronic Hepatitis.) Hepatitis is common throughout the world. Hepatitis can be Acute (short-lived) read more (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 Hepatitis C, Chronic Chronic hepatitis C is inflammation of the liver that is caused by the hepatitis C virus and that has lasted more than 6 months. Hepatitis C often causes no symptoms until after it has badly... read more . The current risk is less than 1 infection for every 2,000,000 units of blood transfused in the United States.
Hepatitis B Hepatitis B, Chronic Chronic hepatitis B is inflammation of the liver that is caused by the hepatitis B virus and that has lasted more than 6 months. Most people with chronic hepatitis B have no symptoms, but some... read more 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.
Blood transfusions rarely transmit syphilis Syphilis Syphilis is a sexually transmitted disease caused by the bacteria Treponema pallidum. Syphilis can occur in three stages of symptoms, separated by periods of apparent good health. It begins... read more . 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.