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Blood Types and Transfusion

Middle schoolBiologyABO and RhD antigens on red cells; plasma antibodies bind matching antigens and clump the cells

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About this experiment

Early blood transfusions often killed the patient, and nobody knew why until Karl Landsteiner discovered blood groups in 1901. Red blood cells carry marker molecules called antigens, and plasma carries antibodies against the antigens a person does not have. If donor cells meet antibodies that fit their antigens, the cells clump together and block blood vessels. Mix donor blood into recipient plasma, build the full compatibility table, and type mystery patients with a test card as a hospital lab does.

Learning goals

  • Describe the antigens and antibodies of the A, B, AB and O blood groups and the RhD factor
  • Explain agglutination as antibodies binding to matching antigens
  • Decide whether a transfusion is safe and explain why
  • Explain why O negative is the universal donor and AB positive the universal recipient
  • Determine a blood type from the results of a typing test

How to use it

  1. 1Give A+ blood to an O+ recipient. Which antibodies does the recipient have, and what happens to the donor cells?
  2. 2Now give O+ blood to an A+ recipient. Why is it safe this way round?
  3. 3Find all the donors an AB+ recipient can receive from. Then find everyone an O− donor can give to.
  4. 4Give O+ blood to an O− recipient, first with the toggle off and then on. Why is the first time still avoided in hospitals?
  5. 5Switch to the typing test. Add blood and read the three wells. Choose the blood type and check your answer.
  6. 6Test several new patients. Make a table of clumping patterns for all eight types.

The model

The rule behind every cell of the table
People make antibodies against the ABO antigens they lack

Assumptions

  • Only red cell transfusions with the ABO and RhD systems are modelled. There are over 40 other blood group systems, which hospitals check by crossmatching.
  • Anti-A and anti-B are present from early childhood. Anti-D is made only after exposure to RhD positive cells.
  • A transfusion counts as safe only when there is no ABO clash and RhD positive blood is not given to an RhD negative person.
  • Plasma transfusions follow the opposite rules (AB plasma is the universal donor) and are not shown.

Try this in class

  1. Q1Which antigens and antibodies does a person with blood group B− have?
  2. Q2Explain why a person with group O can only receive group O red cells.
  3. Q3A sample clumps with anti-B and anti-D but not with anti-A. What is the blood type?
  4. Q4Why do hospitals keep large stocks of O− blood for emergencies?
  5. Q5An RhD negative mother is carrying an RhD positive baby. Why can this be a problem in a later pregnancy?

Frequently asked questions

Why does clumping happen?

Each antibody is Y-shaped with two binding sites, so one antibody can hold on to two cells at once. Many antibodies link many cells into clumps, which can block small vessels and burst, releasing haemoglobin that damages the kidneys.

Which blood type is most common?

It depends on the population. O+ is the most common in many countries, but group B is much more frequent in parts of Asia than in Europe, and RhD negative blood is rare in East Asia.

Is it safe to do blood typing at school?

Most schools no longer test pupils' own blood because of the infection risk. Simulated blood kits or a lab like this one show the same reactions safely.