A blood group (also called a blood type) is a classification of blood, based on the presence and absence of antibodies and inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system. Blood types are inherited and represent contributions from both parents.
The two most important blood group systems are ABO and Rh; they determine someone’s blood type (A, B, AB and O, with +, – or null denoting RhD status) for suitability in blood transfusion. Before you receive a transfusion, compatibility testing is performed between the donated blood and a patient’s blood sample. When a transfusion is given, it is preferable for patients to receive blood of the same ABO and RhD group.
Red blood cell compatibility table
It is a general principle that red cell components of identical ABO group and RhD type as the recipient should be used for transfusion. Group O is the universal red blood cell donor that can be given to all patients, whereas group AB is the red blood cell recipient that can receive blood from any other group.
- Blood group A individuals have the A antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the B antigen. Therefore, a group A individual can receive blood only from individuals of groups A or O (with A being preferable), and can donate blood to individuals with type A or AB.
- Blood group B individuals have the B antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the A antigen. Therefore, a group B individual can receive blood only from individuals of groups B or O (with B being preferable), and can donate blood to individuals with type B or AB.
- Blood group AB individuals have both A and B antigens on the surface of their RBCs, and their blood plasma does not contain any antibodies against either A or B antigen. Therefore, an individual with type AB blood can receive blood from any group (with AB being preferable), but cannot donate blood to any group other than AB. They are known as universal recipients.
- Blood group O individuals do not have either A or B antigens on the surface of their RBCs, and their blood serum contains IgM anti-A and anti-B antibodies. Therefore, a group O individual can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group (i.e., A, B, AB, or O).
| Blood group | Can give blood to | Can receive blood from |
| A+ | A+, AB+ | A+, A-, O+, O- |
| A- | A+, A-, AB+, AB- | A-, O- |
| B+ | B+, AB+ | B+, B-, O+, O- |
| B- | B+, B-, AB+, AB- | B-, O- |
| AB+ | AB+ | Everyone |
| AB- | AB+, AB- | AB-, A-, B-, O- |
| O+ | O+, A+, B+, AB+ | O+, O- |
| O- | Everyone | O- |
Plasma compatibility table
Blood plasma compatibility is the inverse of red blood cell compatibility. Plasma contains anti-A and anti-B antibodies depending upon the blood group. The body also has antibodies to A and/or B antigens according to the blood group. Patients should only receive plasma that does not contain an antibody which could attack the antigens present on their own red cells. Type AB plasma carries neither anti-A nor anti-B antibodies and can be transfused to individuals of any blood group. Type O carries both antibodies, so individuals of blood group O can receive plasma from any blood group.
- Blood group A recipients have A antigen on their red cells, so they can’t receive group O or group B plasma as the anti-A will attack their red cells.
- Blood group B recipients have B antigen on their red cells, so they can’t receive group O or group A plasma as the anti-B will attack their red cells.
- Blood group AB recipients can only receive group AB plasma.
- Blood group O recipients do not have either A or B antigen, so can safely receive plasma of any blood group type.
| Blood group | Can give plasma to | Can receive plasma from |
| A | A, O | A, AB |
| B | B, O | B, AB |
| AB | Everyone | AB |
| O | O | Everyone |
