Blood donation bag. View of a bag containing a donation of blood for use in transfusions. The bag contains about half a litre of blood - an average adult has about 4.5-6 litres of blood. The bag contains an anti-coagulant chemical which prevents the blood from clotting. After donation a sample of the blood will be checked for the presence of infectious diseases such as hepatitis. The blood may be used whole or may be split into its constituents. The oxygen-carrying blood cells may be concentrated and given to someone who has lost a lot of blood. The remaining fluid (plasma) may be given to someone, such as a burns victim, who has suffered a large fluid loss.