Lesson 6 of 9 / Transport in humans
ABO groups and transfusion
Why can group O red cells be compatible with more recipients than group AB red cells?
In this lesson: Work out every ABO donor-recipient combination from antigens and antibodies.
About 5 min
The key ideaA donor red-cell antigen must not meet its matching antibody in the recipient plasma.
This model compares donor red cells with recipient plasma using ABO only. It does not model plasma transfusions or the Rh group.
| Donor | To O | To A | To B | To AB |
|---|---|---|---|---|
| O | Yes | Yes | Yes | Yes |
| A | No | Yes | No | Yes |
| B | No | No | Yes | Yes |
| AB | No | No | No | Yes |
ABO red cells only. Rh and other matching factors are not modelled. This is not a plasma-transfusion table.
Explanation
The four ABO groups are A, B, AB and O. The groups differ in the A and B antigens on their red cell surfaces and the corresponding antibodies in their plasma.
Group A has A antigens and anti-B antibodies. Group B has B antigens and anti-A antibodies. Group AB has both antigens and neither anti-A nor anti-B. Group O has neither A nor B antigen but has both antibodies.
If donor red cells carry an antigen matched by an antibody in recipient plasma, the cells can clump, a process called agglutination. This is why the direction donor -> recipient matters.
For ABO red-cell compatibility, O can donate to O, A, B and AB. A can donate to A and AB. B can donate to B and AB. AB can donate only to AB. Reading in reverse: O receives O only; A receives A or O; B receives B or O; AB receives all four.
These are the syllabus ABO combinations. Actual transfusions require additional matching and testing. Do not apply this red-cell table to donated plasma: plasma contains the antibodies, so its compatibility rules differ.
Step by step
- 1
Read the donor cells
List their A and B antigens, if present.
- 2
Read the recipient plasma
List anti-A and anti-B antibodies, if present.
- 3
Look for a matching pair
A with anti-A, or B with anti-B, makes the pairing incompatible in this model.
Worked example
A donor, AB recipient
Explain why group A red cells are ABO-compatible with a group AB recipient but the reverse pairing is not.
One way to explain it
An AB recipient has neither anti-A nor anti-B, so their plasma does not attack the A antigen on donor cells. In the reverse pairing, AB donor cells carry B antigen, which meets anti-B in the A recipient plasma and can cause agglutination.
Why this answer works
- Keep donor and recipient separate.
- Compare the donor antigens with recipient antibodies.
- Compatibility is not necessarily reversible.
Is this true? "Group O has no antibodies, so it can receive every blood group."
Group O has no A or B antigen on its red cells, but its plasma contains both anti-A and anti-B. In the ABO model it receives O red cells only.