What are blood transfusions?|
Blood transfusions are a useful and lifesaving procedure. But has only become so since the discovery of antigens and antibodies specific to different blood types.
Blood is typed into major and minor groups. The major types are classified by the ABO system, and the rhesus factor.
There are four ABO blood types. These are A, B, AB, and O. The letters A and B stand for different antigens on the red blood cells (RBCs). A person with blood type A has only type antigen, a person with blood type AB has both antigens, and people of blood type O have neither.
Foreign antigens are substances that stimulate the immune system to make antibodies, which attack the antigen. It is extremely important for recipients of blood transfusions that they receive blood that is the same type as their own, otherwise their body's immune system will recognise the donated blood as foreign and attack and destroy it.
The rhesus factor (Rh factor) is another antigen on RBCs. A person who has rhesus factor is Rh positive, a person who does not is Rh negative. If a person has blood type A and is rhesus positive, they are said to have blood type A positive (A+).
Usually, a person can only accept blood of the exact type of their own, but A, B and AB blood types can accept O type blood as it has no antigens. O is called the universal donor, and AB is the universal acceptor, as it can accept all ABO blood types.
There are also several minor classifications of blood types. When a patient has received many transfusions, they start to build an immune response to other minor antigens on RBCs that do not match their own. Some of these include the Kell, Duffy, and Lewis antigens.
The patient may also react to plasma antigens that have attached to the RBCs. To avoid this problem, only washed RBCs are used in transfusion. These are cells that have been rinsed to remove residues of plasma.
Reasons for blood transfusions
- To restore blood volume in patients who have suffered extensive blood loss from hemorrhage, burns, or trauma.
- Anemic patients may require blood transfusions to increase the oxygen carrying capacity of blood.
- People with bleeding disorders due to deficiency in platelets, or blood clotting problems due to deficiencies in coagulation factors may have transfusions to increase their levels of these blood components.
Before donating blood, donors are screened to prevent transmission of disease. People with conditions such as AIDs, cancer, hepatitis, heart disease, malaria, asthma, high blood pressure or bleeding disorders are disqualified from donating blood.
One pint of blood is generally taken (1 pint = 450mls). The average man has 10-12 pints of blood and the average woman has 8-9 pints, and most people can compensate very well with the intake of fluid, and blood volume is quickly restored. The replacement of cells and platelets takes a couple of weeks, so people should not donate blood more frequently than once every two months.
The process of donating blood is very safe. There is no chance of catching infection as only sterile equipment is used. Sometimes people feel lightheaded, and occasionally faint. The donor's blood pressure, pulse rate and temperature is taken to make sure they will not be placing themselves at risk by giving blood. Pregnant women, or people with low blood pressure, or anemia should not donate blood.
Components of blood used in transfusion
Either whole blood or components of blood can be used in transfusion.
- Whole blood - whole blood is used when increases in blood volume and the oxygen-carrying capacity of blood are both needed - usually when the patient suffers from massive blood loss. When only the volume of the blood needs to be increased, other solutions are more likely to be used.