MODEL RELEASED. Blood donation. Nurse inserting a catheter into a vein in the arm of a blood donor. The process of puncturing a vein is called venepuncture. About 475 millilitres of blood will be collected from the donor. This blood will be given to patients in transfusions to replace lost blood, for example during surgery or after accidents. Mobile blood units travel to prearranged places, such as shopping precincts and work places, to allow people to donate blood at their convenience.