To determine ABO blood group and RhD type
When you need to be transfused with blood or blood components or when you donate blood at a donation centre; pregnant women are tested to determine the risk of Rh incompatibility between the mother and foetus
A blood sample taken from a vein in your arm or from a heelprick in the case of an infant
Red blood cells (RBCs) have markers (proteins) or antigens on the surface of the cells. The blood group is determined by which proteins or antigens are present or absent on the red cell surface. Two major antigens or surface identifiers on human RBCs are the A and B antigens. People whose red blood cells have A antigens are considered to be blood group A; those with B antigens are group B; those with both A and B antigens are group AB; and those who do not have either of these markers are considered to have blood group O.
Another important blood group system is RhD. If the D antigen is present on the surface of RBC a person's blood type is RhD+ (positive); if it is absent, the person's blood is type RhD- (negative).
Our bodies naturally produce antibodies against the A and B antigens we do not have on our RBC. For example, a person who is blood group A will have antibodies directed against the B antigens on RBC and someone who is group B will have anti-A antibodies. People with blood group O have both anti-A and anti-B antibodies whereas those with group AB blood do not produce these antibodies.
The following table indicates the type of antibodies a person is expected to have based on their blood type.
|a person with bloodtype ...||will have antibodies to ...|
|O||A and B antigens|
These antibodies are useful for determining a person's ABO group and are significant in defining the types of blood that they can safely receive. For example, if a person who is group A with antibodies directed against the B antigen were to be transfused with blood that is group B, the antibodies would target and destroy the transfused red blood cells, causing severe, potentially fatal complications. Thus it is critical to match a person's blood type with the blood that is to be transfused.
How is the sample collected for testing?
A sample of blood is taken from a vein in your arm or from the tip of your finger (fingerstick). In newborns, blood from the umbilical cord or a small amount of blood from a heelstick may be used for testing.
Is any test preparation needed to ensure the quality of the sample?
No special preparation is needed for this test.
How is it used?
Blood typing is used to determine an individual's blood group and what type of blood or blood components the person can safely receive. It is important to ensure that there is compatibility between a person who requires a transfusion of blood or blood components and the ABO and RhD type of the unit of blood that will be transfused. A potentially fatal transfusion reaction can occur if a unit of blood containing an ABO antigen to which a person has an antibody is transfused to that person. For example, people with blood group O have both anti-A and anti-B antibodies in their blood. If a unit of blood that is group A, B, or AB is transfused to this person, the antibodies in the person's blood will react with the red cells, destroying them and causing potentially serious complications.
If an RhD-negative individual is transfused with RhD-positive blood, it is likely that the person will produce antibodies against RhD-positive blood. Although this does not cause problems for the person during the current transfusion, a future transfusion with RhD-positive blood could result in a serious transfusion reaction.
RhD typing is especially important during pregnancy because a mother and her foetus could be incompatible. If the mother is RhD-negative but the father is RhD-positive, the foetus may be positive for the RhD antigen. The mother’s body could develop antibodies against the RhD antigen. The antibodies may cross the placenta and cause destruction of the baby’s red blood cells, resulting in a condition known as haemolytic disease of the foetus and newborn. This is a particular risk in subsequent pregnancies.
To prevent development of RhD antibodies, an RhD-negative mother is treated with an injection of RhD immune globulin during her pregnancy and again after delivery if the baby is RhD-positive. The RhD immune globulin binds to and “masks” any RhD antigen from the foetus that the mother may be exposed to during her pregnancy and delivery and prevents her from becoming sensitised and developing antibodies against the RhD antigen.
Blood typing is also used to determine the blood group of potential donors at blood donation centres. Units of blood that are collected from donors are blood typed and then appropriately labelled so that they can be used for people that require a specific ABO group and Rh type.
When is it requested?
ABO grouping and RhD typing are performed on all donated blood. They are also performed for all people who require a blood transfusion. Cases in which blood or blood products are needed for treatment may include:
- Severe anaemia and conditions causing anaemia such as sickle-cell disease and thalassaemia
- Surgical patients with intra-operative or post-operative bleeding
- Injury or trauma
- Patients with excessive blood loss
- Cancer and the effects of chemotherapy
- Bleeding disorders such as haemophilia
All pregnant women should be tested to determine whether they are RhD negative or positive. All newborns of RhD negative mothers should also be tested to determine if the mother needs to receive RhD immune globulin.
What does the test result mean?
The results of blood typing will determine if a person is group A, B, AB, or O and if he or she is RhD negative or positive depending on what antigens are present on the person's RBC. The results will tell the clinician what blood or blood components will be safe for the person to receive.
Blood group and Rh type Can safely receive blood that is... A positive A positive, A negative, O positive, O negative A negative A negative, O negative B positive B positive, B negative, O positive, O negative B negative B negative, O negative AB positive AB positive, AB negative, A positive, A negative, B positive, B negative, O positive, O negative AB negative AB negative, A negative, B negative, O negative O positive O positive, O negative O negative O negative
The results will tell a pregnant woman whether she is RhD positive or negative and whether she may be a candidate for receiving RhD immune globulin to prevent her from potentially developing antibodies against her foetus' blood cells.
Blood typing will also tell the personnel at a blood donation centres what blood type a person is donating and who can safely receive that blood.
Is there anything else I should know?
The following table summarises the approximate distribution of blood groups and types in the UK population:
Blood Type Rh POSTIVE Rh NEGATIVE total O 37% 7% 45% A 35% 7% 40% B 8% 2% 11% AB 3% 1% 4% TOTAL 83% 17% 100%
Do I need to know my blood group?
Your blood will always be typed before you receive any blood to make sure that it is safe for you. The only time blood is given without blood typing is if there is an extreme emergency and there isn't enough time to perform the test before the blood needs to be transfused. In this case, group O, RhD negative blood (the universal donor blood) is administered since this blood type does not have any A, B, or RhD antigens that can potentially cause a haemolytic transfusion reaction.
Who is a universal blood donor and a universal blood recipient?
A universal blood donor is someone who has an O blood type and is RhD negative. This means that they have no A or B antigens or RhD factor on their red blood cells. Their RBC can be given to a person with any ABO or RhD blood type, because there are no A, B, or RhD factor antigens on the donors red blood cells for the antibodies of a person with a different blood type to react with. Hence, there is no potential for a haemolytic transfusion reaction due to ABO or RhD incompatibility. A universal recipient is a person who has an AB blood type and is RhD positive. They can receive red blood cells of any ABO or RhD type with no risk of a serious haemolytic transfusion reaction due to ABO or RhD incompatibility.
Besides ABO and RhD, are there other types of red blood cell antigens?
Yes, there are numerous other antigens present on the surface of red blood cells. These minor RBC blood group antigens include, for example, Kell, Kidd, Duffy, and other RhD antigens. Antibodies to these antigens are not made naturally and are only produced by the body when exposed to them through blood transfusion or when a mother is exposed to a baby's blood cells during pregnancy. These antibodies are not detected with routine blood grouping but may be found with an indirect antiglobulin test. For more on these, see the article on RBC Antibody Identification.