Red blood cells carry markers called antigens on their surface. Your blood type depends on which antigens you have, and your plasma carries antibodies against the ones you lack.
ABO groups
Type A has A antigens, type B has B, type AB has both and type O has neither. Plasma naturally contains antibodies against the missing antigens, so type A plasma attacks type B cells.
Rh factor
Rh-positive cells carry the D antigen; Rh-negative cells do not. An Rh-negative person makes anti-D only after exposure through transfusion or pregnancy, which is why Rh-negative mothers receive anti-D immune globulin.
Universal donors and recipients
O negative red cells can go to almost anyone in an emergency because they carry no A, B or D antigens. AB positive patients can receive red cells of any ABO and Rh type.
Transfusion reactions
Giving the wrong ABO type makes the patient's antibodies destroy the donor cells within minutes. Signs include fever, chills, back pain, low blood pressure and dark urine.
| Patient type | Antibodies in plasma | Can receive red cells from |
|---|---|---|
| O | Anti-A and anti-B | O |
| A | Anti-B | A, O |
| B | Anti-A | B, O |
| AB | None | AB, A, B, O |
At the bedside
Before every transfusion, two staff check the patient's identity against the unit at the bedside, and the patient is watched closely in the first 15 minutes. If a reaction starts, stop the transfusion, keep the IV open with saline and call for help.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).