Donated blood. Bags of donated blood. Each bag has a unique bar code that can be used to identify the donor. Samples of the blood will be screened for blood diseases, such as hepatitis and HIV, and typed for blood group. This is essential before the blood can be used. Blood can either be stored whole or be separated into different blood components. Donated blood is used in transfusions to patients who have lost blood, for example during surgery or in accidents.