Certain criteria will keep you from becoming a donor. For example, donors are screened for age (you must be at least 17 years old to donate blood) and weight (you need to weigh at least 110 pounds [50 kilograms] to be a donor). The average human has about 10 to 12 pints of blood circulating throughout the body at any given time, which is about 7 percent of your total body weight. Donors who weigh between 110 and 149 pounds (50 and 68 kilograms), for example, are allowed to donate a volume of 1.5 pints (705 milliliters) of plasma while the volume of donated blood plasma for those who weigh 175 pounds (79 kilograms) or more is as much as 2 pints (903 milliliters) -- your weight determines how much you can safely give [source: Access Clinical].
Donors should expect a physical examination and medical history review during their first plasma donation visit. During each subsequent visit, expect a review of your medical history and a check of your vital signs (blood pressure, pulse and temperature); a quick finger prick may be performed to test for anemia and your protein levels. Donors are asked questions about their history with hepatitis, cancer or other major illness or surgery listed on the FDA's medical deferral list -- whether they've had a fresh tattoo, piercing, acupuncture session or any needle stick within the last year (depending on the state where you live), as well as personal habits, travel habits and residency. You'll have to wait a year upon returning home to donate blood if you've traveled to an area known as a malaria risk, such as Central Asia or Africa, for instance. Pregnant women may donate six weeks after the end of the pregnancy (donating while nursing is OK).
Thirteen tests are performed on all donated blood, including: ABO blood grouping and Rh type, cholesterol, hepatitis (hepatitis B surface antigen, hepatitis B core antibody, and hepatitis C antibody), HIV (HIV-1 antibody, HIV-2 antibody, and HIV-0 antibody), HTLV (Human T-Lymphotrophic Virus Type I and II antibodies), red cell antibody screen, West Nile virus and syphilis [source: Carter BloodCare]. The test results of donated blood screening tests are confidential; the donor is notified of any positive results, and blood donation is delayed (or denied). No donated blood that tests positive during the screening procedures is used.