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 RhD incompatibility between the mother and fetus
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 heel-stick may be used for testing
No test preparation is needed
Red blood cells (RBCs) have substances known as antigens on the surface of the cells, that are capable of triggering an immune response. The genes you inherit from each parent will determine the red cell antigens you express on your red cells. Blood grouping is based on performed by using commercial antisera to detect red cell antigens present on the surface of the red cells.
The two most clinically significant blood group systems are ABO and RhD.
The ABO blood group system involves two major red cell surface antigens,the A and B antigens. There are 4 main blood groups defined by the ABO system:
1. Blood group A – A antigens are present on RBCs
2. Blood group B – B antigens are present on RBCs
3. Blood group AB – both the A and B antigens are present on RBCs
4. Blood group O – neither the A or B antigens are present on RBCs
Our bodies will naturally produce antibodies against the A and B antigens we do not have on our RBCs. For example, a person who is blood group A will have naturally occurring anti-B antibodies present in their blood plasma, and someone who is group B will have anti-A antibodies present in their plasma. Individuals who are blood group O have both anti-A and anti-B antibodies present whereas those who are group AB do not produce any antibodies against the A or B antigens.
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 ...
|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. Therefore, it is critical when selecting blood for transfusion purposes to ensure that ABO compatible blood is transfused with group O being considered as the universal donor regarding the ABO group.
The Rh blood group system involves the RhD red cell surface antigen. If the RhD 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). The RhD status is commonly added after the ABO group status to determine suitability for blood transfusions e.g if a person has the A and RhD antigens present on their RBCs, the blood type is defined as A positive (A+); if a person did not have any A, B or RhD antigens present the blood type is defined as O negative (O-). After the ABO blood system, the Rh system is considered the next most clinically significant & most likely to be involved in transfusion reactions that cause destruction of red cells (known as a haemolytic transfusion reaction).
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 life-threatening complications.
Rh antibodies are different to ABO antibodies in that they only develop if an RhD-negative individual is exposed to RhD antigens via transfusion, pregnancy or organ transplantation and can lead to haemolytic transfusion reactions.
RhD typing is especially important during pregnancy because a mother and her fetus could have differing RhD antigen status. If the mother is RhD-negative but the father is RhD-positive, the fetus may inherit the RhD antigen from the father. The mother’s body could develop antibodies against the RhD antigen, through exposure to the fetus red blood cells. This is known as sensitisation and can cause serious risks in future pregnancies. If sensitisation occurs, and the woman becomes pregnant with another RhD-positive baby, the RhD antibodies present in her blood can cross the placenta and cause destruction of the baby’s RhD-positive red blood cells, a condition known as haemolytic disease of the fetus and newborn (HDFN).
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 (administration of prophylactic anti-D). The RhD immune globulin binds to and “masks” any RhD antigen from the fetus 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 e.g. occurring through childbirth
- 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 their RBCs. The results will inform the clinician on what blood or blood components will be safe for the person to receive through a blood transfusion.
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
Group O, RhD-negative blood (O-) can safely be given to anyone as it does not have any A, B or RhD antigens on the surface of the cells and is compatible with every other ABO and RhD blood group. It's often used in medical emergencies when the blood type of the patient is not immediately known. In cases of pregnancy, blood group typing will inform a clinician on whether a pregnant woman 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 fetus' blood cells. It is also important to note that RhD-negative women of child-bearing age should only receive RhD-negative blood if they require a blood transfusion, to prevent the risk of RhD sensitisation occurring. Blood typing will also tell the personnel at a blood donation centre what blood type a person is donating and who can safely receive that blood.
Is there anything else I should know?
Do I need to know my blood group?
Your blood will always be typed before you receive any blood transfusion 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. To date there are currently 44 blood group systems identified that correspond to 354 red cell antigens. Within the Rh system, there is further Rh antigens alongside RhD, including C, c, E and e that are present on the red cell surface and are clinically significant in blood transfusions. Further recognised blood group systems that are clinically significant include Kell, Kidd Duffy and MNS. 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.