The donor's blood type must be determined if the blood will be used for transfusions. The collecting agency usually identifies whether the blood is type A, B, AB, or O and the donor's Rh (D) type and will screen for antibodies to less common antigens. More testing, including a crossmatch, is usually done before a transfusion. Group O is often cited as the "universal donor" but this only refers to red cell transfusions. For plasma transfusions the system is reversed and AB is the universal donor type.

The most common method is collecting the blood from the donor's vein into a container. The collected blood is typically separated into parts, usually red blood cells and plasma, since most recipients need only a specific component for transfusions. The blood is usually stored in a plastic bag that also contains sodium citrate, phosphate, dextrose, and sometimes adenine. This combination keeps the blood from clotting and preserves it during storage.

Donors are usually kept at the donation site for 10-15 minutes after donating since most adverse reactions take place during or immediately after the donation. Blood centers typically provide light refreshments such as tea and biscuits or a lunch allowance to help the donor recover.