Curriculum · Hematology
ABO blood groups: antigens, antibodies and genotypes
What it is
The ABO group is found by testing the patient's RBCs for the A and B antigens, and the Rh (D) group by testing the same RBCs for the D antigen. Each of those two takes 5 minutes. Everything else in the routine transfusion medicine tests is built on top of them: the antibody screen looks for RBC alloantibodies, and the crossmatch puts donor RBCs against the recipient's own plasma or serum.
How it is diagnosed
The routine transfusion medicine tests, with the time each takes:
- ABO group, 5 minutes: patient RBCs tested for A and B antigens
- Rh (D) group, 5 minutes: patient RBCs tested for D antigen
- Antibody screen, 45 minutes: screens for RBC alloantibodies formed as a result of prior transfusion or pregnancy
- Antiglobulin crossmatch, 45 minutes: mandatory for patients with RBC alloantibodies, and it incubates donor RBCs, recipient plasma or serum, and anti-IgG
- Immediate spin crossmatch, 5 minutes: mixing of donor RBCs and recipient plasma or serum, used to verify ABO compatibility only, and only for patients with a negative antibody screen and no history of RBC alloantibodies
For infants less than 4 months of age, initial testing must include ABO and Rh (D) group.