Blood is a living tissue that is pumped through the heart and circulates throughout the body via the arteries, veins and capillaries. Blood transports essential substances, including electrolytes, hormones, vitamins, antibodies and oxygen, between organs and tissues to meet the body's metabolic needs. Blood also removes carbon dioxide, the waste product generated by the body's metabolic activity, from the body's tissues. The carbon dioxide passes through the veins to the lungs, where it is expelled into the exhaled air. Any operation entails a certain amount of blood loss, but in most cases this does not necessitate a blood transfusion. However, about 14 percent of all people who undergo surgery require blood transfusions, and many surgeries could not be performed without transfusion support. Emergency transfusions are for people who suffer major trauma, such as car accidents, account for far more transfusions during surgery than planned transfusions. Although blood units are still kept in reserve during major surgery, transfusions are less frequently performed because of the advances in surgical techniques that have reduced blood loss and made less invasive procedures possible. Blood transfusion is safe only when the donor's blood and the blood of the recipient are compatible. There are four main blood groups (A, B, AB and O) and each is divided into two Rh types, Rh-positive and Rh-negative. The surface of each red blood cell is coated with proteins known as antigens that differ for each blood type. Because each of us forms antibodies against the antigens our bodies lack, it is important that transfused and native blood match. Before any transfusion, small amounts of the donor blood and the recipient's blood are mixed in a lab to be sure they are compatible. Blood may be transfused as whole blood, or one or more of its components may be transfused. Blood transfusions can be life-saving but, as with any treatment, there are risks involved. These risks include hemolytic reaction (a breakdown of red blood cells that usually results in anemia) because of incompatibility, the transmission of disease, fever and allergic reactions. The most common infection transmitted by blood transfusion is hepatitis C, but the risk of this transmission is less than 1 in 3,000 per unit of blood or blood product. The risk of transmission of the HIV is between 1 in 40,000 and 1 in 225,000 per unit of blood or blood product. Overall, the risk of contracting any infection from a blood transfusion is extremely low. All donated blood is screened for possible infectious diseases. Before 1985 blood was tested only for hepatitis B and syphilis, but now each unit of donated blood undergoes eight tests for infectious diseases, including HIV and hepatitis C. The test for HIV, the monoclonal HIV-lp24 antigen test, can detect the virus more quickly, thus further assuring the safety of the blood supply. The safest blood of all, however, is still your own. The most common immunologic complication that occurs because of a blood transfusion is fever and chills. Almost all deaths that occur because of blood transfusion are due to blood type incompatibility, which can occur because of an error in patient identification. If you are preparing to have surgery, make sure you know your blood type and that your patient identification bracelet identifies you correctly. Double-check with your doctor if you have any doubts. The most common reason for a blood transfusion is to replace blood volume. In a healthy person the body will naturally replace blood volume, even when moderate blood losses occur during surgery, but in people with preexisting conditions or who experience significant blood loss during surgery, transfusion may prove necessary. In discussing your upcoming surgery, review the possible need for blood transfusion with your doctor. You will want to discuss why a transfusion might be necessary. Last Updated: 10/1/2002
The Johns Hopkins University 1996-2003. All rights reserved. This information is not intended to provide advice on personal medical matters, nor is it intended to be a substitute for consultation. |
