Blood grouping

• Start with basics! Even if you aren’t aware of how antibodies are used to determine blood groups, talk about the ABO classification → i.e. you can have blood types A, B, AB or O

• Once you have listed the blood types, you can then think about why these specific blood types exist, and what these letters mean.

• Blood groups classify red blood cells based on surface antigens, which are protein molecules found on the surface of red blood cells

How does the ABO classification system work?

• In the ABO classification system, the surface antigen present is what determines your blood group. e.g. A antigens means you are type A, B antigens means you are type B.

• If your body has antigens for both A and B, then you are blood type AB (rarest).

• If however, you don’t have either A or B antigens for your blood type, then your blood type is O. Instead of antigens, your body produces antibodies against A or B antigens.

• The immune system creates antibodies against the antigens you don’t have, so for example type O blood has no antigens and therefore has anti-A and anti-B antibodies

Type A: A antigen, anti-B antibodies 

Type B: B antigen, anti-A antibodies 

Type AB: both antigens, no antibodies 

Type O: no antigens, both antibodies 

• The student should explain that this is important as it determines compatibility for transfusions

• The patient’s blood group must be matched to that of the donor, and it should also be cross matched to prevent transfusion reactions

• Blood is further categorised using the Rhesus system, which looks at the presence  (Rh+) or absence (Rh-) of D antigen 

• Think from first principles! In order to give universal blood, you want to try and give blood that will not cause an antibody response in the donor.

• Prompt: Think about which blood group has no antigens on its surface…

Answer

• Type O could be used for all transfusions, as there are no antigens (ABO or Rh) on the surface of RBCs

• If there are no surface antigens, then the recipient will not create an antibody response against the donor blood

• Individuals who are blood group O are considered universal donors

Extension question: What would happen if you gave group B blood to a group A patient?

• The donor group B blood contains group B antigens, which the group A patient will recognise as foreign.

• As a result, the group A patient will generate an antibody response against the donor group B antigens

• If antibodies were to bind donor B antigens, this causes agglutination, where the red blood cells (RBCs) clump together, and haemolysis, where the RBCs are broken down and destroyed

Say what you see! → start by describing the experimental setup and what you think is going on

• This appears to be the results of some sort of cell assay.

• There are two sets of results, one from a ‘not agitated’ group and another from an ‘agitated’ group.

• In each set of results, you can see that there are Anti-A and Anti-B antibody columns on the left (y-axis), and the blood groups of the cells used in the experiments across the top (x-axis).

• Summary: thinking about the previous questions, it looks like a cell assay which is testing the differences between the antibody responses of Anti-A antibodies and Anti-B antibodies across a variety of blood groups (AB, A, B, O, P, Me).

• In this case, P could possibly stand for ‘Patient’ and ‘Me’ → could suggest that this assay is being used for donor antibody testing in a patient for cross-matching.

Can you try to explain/interpret the results above?

• The student should identify that on the left, we can see that either anti-A or anti-B antibodies have been added to each row of wells. Each column has different blood types added, and the fifth column has the patient sample 

• Describe that when antibodies react with the corresponding antigen, this causes agglutination  → this can be seen as the wells have large circles, which when agitated become broken up 

• Identify examples e.g. type AB blood has A + B antigens, so both anti-A and anti-B antibodies cause agglutination, while type O blood has no antigens so neither antibody causes agglutination 

• Describe that in the patient blood sample, agglutination is observed with the anti-B antibodies only, showing the patient has B antigens on their RBCs → they have group B blood 

• In the ‘Me’ sample, agglutination is observed with the anti-A antibodies only, showing that ‘Me’ has A antigens → they have group A blood

• In this case, the patient cannot be used as a donor to give blood for ‘Me’