Blood Groups

Public summary: 

What are 'blood groups'? Why is it important to match blood groups for transfusion? Find out with our colourful demonstration.

Why are blood groups important?
Useful information
Kit List: 

Red and blue food colouring
Plastic droppers
20ml Universal containers
4 well plates
Laminated cells and antibodies – A antigens are red and triangular, B green and semi-circular, RhesusD orange and squarish. The antibodies have corresponding shapes.

Frequency of use: 

In a nutshell:
Talk about different blood groups and why it is important to match blood for transfusion. Demonstrate how different blood groups are compatible using the food colouring, and use the laminated cells and antibodies as props for explanation.
How to set up the experiment:
Make up some A, B, AB and O ‘blood’ in the universal containers as follows:
A: 2 drops red food colouring in 20ml water
B: 4 drops blue food colouring in 20ml water
AB: 2 drops red and 4 drops blue colouring in 20ml water
O: water

Take four 4-well plates and lay them out in a square. Put about 1ml of A blood in each of the 4 wells in the first column, 1ml of B in the second, 1ml of AB in the third and 1ml of O in the fourth column. These represent the recipient blood.
You can then get the children to add about 4 drops of each blood type from the 20ml tubes to each of the types in the plates (so add 4 drops of A to each of the wells in the top row, 4 drops B to each in the second row etc). These represent the donor blood. It is worth testing this at first to check that your colouring concentrations give the results that you want! The idea is that if the colour of the ‘blood’ in the well changes, the blood groups are incompatible. If it doesn’t change, they are compatible. For example, adding B (blue) blood to AB (purple) will not cause a colour change, but adding B to O (clear) will.
The laminated cells and antibodies can be laid out in areas corresponding to each blood group. The contents of one area can then be transferred into another area (a transfusion) and any matches between the antibodies/antigens observed.

Background information:
The most important blood groups in transfusion are the ABO blood group system and the RhD blood group system.
Blood groups are determined by a protein (antigen) on the surface of the red cell. So, the ABO system has A and B antigens and the RhD system has the D antigen.
In all, there are 30 major blood group systems. This means a person may be A RhD positive, and at the same time Kell (Kell system) positive, M and N (MNS system) positive and Lea and Leb (Lewis system) positive.

The ABO blood group system
If you have blood group A then you have got the A antigen on your red cells.
Blood group B means you have the B antigen, while group O has neither, and group AB has both A and B antigens.
The ABO system has associated anti-A and anti-B antibodies, antibodies being the body's natural defence against foreign antigens. These antibodies are found in the plasma.
Blood group A has the A antigen. This group recognises the B antigen as foreign and can make anti-B antibodies.
Similarly, blood group B has the B antigen and therefore recognises the A antigen as foreign and can make anti-A antibodies against the A antigen.
Group AB has both the A antigen and the B antigen so this group makes no antibodies.
Group O has neither A nor B antigen so blood from this group can be given safely to any other group. This is why Group O donors are known as "universal donors". Group O individuals can make both anti-A and anti-B antibodies if exposed to these antigens so can't receive blood from either.
Giving someone blood from the wrong ABO group could be life-threatening.
For instance, the anti-A antibodies in group B attack group A cells and vice versa. This is why group A blood must never be given to a group B person.

*remember the rules below apply to transfusions of packed red blood cells - so no donor antibodies are transferred to the recipient as these are in the plasma*
Blood group AB individuals have both A and B antigens on the surface of their RBCs, and their blood plasma does not contain any antibodies against either A or B antigen. Therefore, an individual with type AB blood can receive blood from any group (with AB being preferable), but cannot donate blood to either A or B group. They are known as universal recipients.
Blood group A individuals have the A antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the B antigen. Therefore, a group A individual can receive blood only from individuals of groups A or O (with A being preferable), and can donate blood to individuals with type A or AB.
Blood group B individuals have the B antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the A antigen. Therefore, a group B individual can receive blood only from individuals of groups B or O (with B being preferable), and can donate blood to individuals with type B or AB.
Blood group O (or blood group zero in some countries) individuals do not have either A or B antigens on the surface of their RBCs, but their blood serum contains IgM anti-A and anti-B antibodies against the A and B blood group antigens. Therefore, a group O individual can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group (i.e., A, B, O or AB). If a patient in a hospital situation were to need a blood transfusion in an emergency, and if the time taken to process the recipient's blood would cause a detrimental delay, O Negative blood can be issued. They are known as universal donors.

What about plasma?
Plasma is the liquid component of blood that doesn't contain any cells. Recipients can receive plasma of the same blood group, but otherwise the donor-recipient compatibility for blood plasma is the converse of that of RBCs - plasma extracted from type AB blood can be transfused to individuals of any blood group because it won't contain any antibodies against A or B antigens; individuals of blood group O can receive plasma from any blood group; and type O plasma can be used only by type O recipients.

The RhD system
Another important blood group system in transfusion is the RhD system.
85% of people have the D antigen on their red blood cells and are RhD positive.
The remaining 15% lack the D antigen and are RhD negative.
Your blood group is defined by your ABO group together with your RhD group. For instance, someone who is group A and RhD negative is known as A negative.
The chart below explains the national distribution of blood groups. Click on a blood type for more information.
ABO Blood Group Rh(D) Type Percentage of Population with this Group
O +
Pos 37%
O -
Neg 7%
Total Blood Type O 44%
A +
Pos 35%
A -
Neg 7%
Total Blood Type A 42%
B +
Pos 8%
B -
Neg 2%
Total Blood Type B 10%
AB +
Pos 3%
AB -
Neg 1%
Total Blood Type AB 4%
Total Pos 83%
Total Neg 17%

Why is the Rhesus system important for pregnant ladies?
Unlike A and B antibodies, RhesusD antibodies are not found in people who are RhesusD negative. Therefore they won’t react to RhesusD positive blood unless they have already been sensitised. If a RhD- mother has a RhD+ foetus (only possible if the father is RhD+), feto-maternal transfusion may occur during pregnancy/childbirth, causing the mother to produce anti-RhD antibodies. If the mother subsequently has a second Rh+ pregnancy, the anti-RhD antibodies can cross the placenta and cause agglutination and degradation of the red blood cells in the foetus. This causes ‘haemolytic disease of the newborn’, features of which include enlarged liver, spleen or heart in the foetus and anaemia, jaundice, enlarged organs and difficulty breathing in the newborn. To prevent this, RhD- mothers can be given IgG anti-D antibodies by intramuscular injection. These antibodies then cause destruction of foetal RhD+ blood cells before the maternal immune system can react to them. These are administered at 28 weeks of pregnancy, sometimes 34 weeks and within 72 hours of birth. This is passive immunity and wears off after 4-6 weeks so treatment is required with each pregnancy.

Why do people have antibodies against the A and B antigens if they don’t have those antigens themselves?
It's thought that blood groups are very similar to some bacterial/food sugars which act as antigens so you get cross reactivity. Because ABO antigens are expressed quite widely in tissues (all endothelium and all epithelial cells, and other cell types express the H antigen which is a precursor and can still react with antibody) your natural tolerance mechanisms kick in to protect the sugar you do have, but obviously not to the ones you don't.

How can blood group be used to determine paternity?
BE CAREFUL discussing this! Do not ask the parents for their blood groups!
ABO inheritance patterns
The ABO blood group system is determined by the ABO gene, which is found on chromosome 9. The four ABO blood groups, A, B, AB and O, arise from inheriting one or more of the alternative forms of this gene (or alleles) namely A, B or O.
Genetic Combinations of ABO Blood Groups
Blood group Possible genes
A AA or AO
B BB or BO
The A and B alleles are codominant so both A and B antigens will be expressed on the red cells whenever either allele is present. O alleles do not produce either A or B antigens, thus, are sometimes called ‘silent' alleles.

ABO Inheritance Patterns
Parental blood groups Child's blood group
O and O O
O and A O or A
O and B O or B
O and AB A or B
A and A A or O
A and B O or A or B or AB
A and AB A or B or AB
B and B O or B
B and AB B or A or AB
AB and AB A or B or AB
Note: These are various possible blood groups that children may inherit according to the combination of parental blood groups.

Risk Assessment
Date risk assesment last checked: 
Sun, 26/01/2020
Risk assesment checked by: 
Date risk assesment double checked: 
Mon, 27/01/2020
Risk assesment double-checked by: 
Beatrix Huissoon
Risk Assessment: 

Using simple food colouring solutions to explain blood group compatibility.

Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Spillages Slip hazard. 2 2 4 All spills should be cleared up immediately, get children to be careful using pipettes. Call first aider in case of injury. Use wet floor sign if necessary. 1 2 2
Fake blood Feeling faint at sight of fake blood/ discussion of blood. 2 3 6 Remind people that the blood isn't real and ask them to tell you if they feel faint. Chair nearby for light-headed-feeling people. Call first aider in case of injury. 2 2 4
Experiment photos: