Blood bank. Hand removing a blood bag from a refrigerated hospital blood bank. Generally, around half a litre of blood is drawn from a donor into a plastic bag containing an anticoagulant to prevent the blood from clotting. The blood is classified according to its group, tested for blood-borne diseases, and stored either whole or, as here, separated into its different components. This bag contains group O, Rh (Rhesus) negative red blood cells in an additive solution.