HEALTH / Common Procedures: Blood transfusions

SOMEONE who has lost a lot of blood in an accident or from internal bleeding from the stomach or intestines will recover most quickly and surely if the amount of blood lost is put back into a vein - a blood transfusion.

Attempts at blood transfusion in the 19th century were mostly disastrous. When blood from animals and most human blood was put into the circulation, it provoked acute illness which often led to fatal kidney failure. Sometimes, however, human blood did not cause a reaction, and at the beginning of the 20th century the Austrian pathologist Karl Landsteiner showed that human blood could be divided into four main types - A, B, AB, and O. If someone is given blood of their own type the chances of a reaction are much reduced. The remaining risk can be virtually eliminated by mixing together in the laboratory samples of blood from the donor and the recipient, a test known as cross matching.

Once these principles were established, blood transfusion became an essential part of medicine. In the 1920s and 1930s it helped remove the main risk of death in childbirth and it remains the first step in the resuscitation of victims of road accidents and war injuries. Much complex surgery, such as coronary artery bypass operations and joint replacements, relies on blood transfusion. Repeated transfusions are needed to maintain the health of people with chronic disorders such as thalassaemia.

Despite research, no satisfactory substitute has been found for human blood, and around the world blood is collected from donors and stored in banks. Some countries follow the British example of relying on volunteer donors, while in others donors are paid. The science of blood transfusion has advanced a great deal since Landsteiner's time; 21 blood group systems are now recognised, and though groups such as the Lewis and MNS systems are not usually of practical significance they sometimes cause problems in patients who need repeated transfusions. The main problem for blood transfusion services, however, is infection.

A blood donor may feel healthy but his or her blood may contain malaria parasites, syphilis bacteria, one or more of the viruses causing hepatitis, or the human immunodeficiency virus (HIV), the cause of Aids. Health screening of donors, and tests on donated blood can reduce the risks of these infections being transmitted to very low levels, but cannot eliminate them. With HIV there is a period of several weeks between infection and the antibody test becoming positive, and if blood is given during this period it may contain the virus. The estimate for the risk of a blood transfusion transmitting HIV is one in a million in Britain but about one in 60,000 in the United States.

So long as these risks continue, surgeons will be looking for ways of reducing the need to transfuse donated blood. Two methods have been found. Patients on a waiting list for surgery can donate several pints of their own blood in the weeks before the operation, and this can be stored until needed. During surgery blood can be salvaged from the operation site, cleaned, and returned to the patient. Giving blood is altruistic; it has no drawbacks or risks; and anyone who has not come forward as a donor should ask themselves why not.