Quick answer
Red cells carry antigens; plasma carries antibodies. For a plasma transfusion, the donor's antibodies must not attack the recipient's red cells. That flips the familiar chart: AB plasma (no antibodies) can go to anyone, while O recipients (no antigens) can accept plasma from anyone. Rh factor is generally not a concern for plasma.
ABO plasma compatibility chart
| ABO group | Antibodies in plasma | Can give plasma to | Can receive plasma from |
|---|---|---|---|
| A | anti-B | A, O | A, AB |
| B | anti-A | B, O | B, AB |
| AB | none | A, B, AB, O | AB |
| O | anti-A, anti-B | O | A, B, AB, O |
Why plasma rules are reversed
When you receive red cells, the danger is that your antibodies attack the donor's cells. When you receive plasma, the danger is that the donor's antibodies attack your cells. The same underlying biology, viewed from the opposite side, produces a mirror-image chart.
Type O plasma contains both anti-A and anti-B, so it is only safe for type O recipients. Type AB plasma contains neither, so it is safe for every ABO group. Type A plasma (anti-B) suits A and O recipients; type B plasma (anti-A) suits B and O recipients.
What about Rh factor?
Plasma contains very few red cells, so the RhD antigen is not normally a concern in plasma transfusion. Anti-D antibodies are only present in the plasma of Rh-negative people who have been sensitised, and such donors are usually screened out. In practice, plasma is matched on ABO alone in most settings.
Plasma products and platelets
The rules above apply to fresh frozen plasma and similar products. Platelets are suspended in plasma, so ABO compatibility is preferred for platelet transfusions too, though out-of-group platelets are sometimes given when supply is limited. Whole blood, which contains both red cells and plasma, must satisfy both directions and is therefore usually given type-specific.
Compare with the red cell compatibility chart.