A blood transfusion is carried out to treat severe anaemia or to replace blood lost by bleeding. It is performed in hospital, sometimes on a day patient basis. The amount of blood required depends on the severity of the condition. Each bag of blood is usually given over a 3–4 hour period, but it can be given more quickly if necessary. A blood sample is taken first to check that your blood is compatible with blood taken from donors (a process called cross-matching). The donor blood is screened for infectious organisms such as HIV and the hepatitis viruses and is stored in blood banks. Sometimes only a particular component of blood is transfused, such as red blood cells or platelets.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.