MODEL RELEASED. Blood donation. Nurses and blood donors at a blood donation session. The nurse (left) is preparing to collect blood from the woman lying on the bed. A tube will be inserted into the donor's forearm to collect blood. Usually about 475 millilitres of blood is collected. Mobile blood units travel to prearranged areas, such as shopping centres and work places, so that potential blood donors can attend at their convenience. Donor blood is given to patients in transfusions to replace lost blood, for example during surgery or after accidents.