Specially trained technical staff members are available at each blood collection center, and the details of each donor's health and activities are discussed in a confidential setting prior to blood donation. To ensure the safety of blood donation for both donors and recipients, all volunteer blood donors must be evaluated to determine their eligibility to give blood. The final determination of eligibility is made at the time of donation
Although all blood is made of the same basic elements, not all blood is alike. In fact, there are eight different common blood types, which are determined by the presence or absence of certain antigens—substances that can trigger an immune response if they are foreign to the body.
Since some antigens can trigger a patient's immune system to attack the transfused blood, safe blood transfusions depend on careful blood typing and cross-matching. There are four major blood groups determined by the presence or absence of two antigens, A and B. These include: