Blood donation

Blood donation is when a person voluntarily gives blood, which can be used for blood transfusions or to make certain drugs. Blood banks store this blood. The blood can be used to help the victims of accidents, for example. Usually, the blood donor and the donated blood are tested for diseases which spread through the blood. These include various forms of Hepatitis,HIV and Syphilis. Usually, a series of questions also need to be answered to make sure that there is no risk to the person donating. 
A special case of blood donation sometimes occurs before a dangerous medical operation. People donate their own blood, which can be used after the operation if they lose too much blood.