Curriculum · Hematology
Pre-transfusion testing and crossmatching
What it is
The routine transfusion medicine tests done before red blood cells are given:
- 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 involves incubation of donor RBCs, recipient plasma/serum and anti-IgG
- Immediate spin crossmatch, 5 minutes: mixing of donor RBCs and recipient plasma/serum, used to verify ABO compatibility only, for patients with a negative antibody screen and no history of RBC alloantibodies
The order runs ABO group, then Rh (D) group, then antibody screen, then an antiglobulin crossmatch or an immediate spin crossmatch or a computer crossmatch.
How it is diagnosed
The blood bank investigations to order before red cells are given are the blood group (ABO typing), the antibody screen, and the cross match (compatibility testing). Two separate samples from 2 different venipunctures are needed when this is the patient's first admission in the hospital and there are no historical blood bank investigations, so that 2 blood samples ensure double checking of blood group before labeling it to the patient. The principle of the cross match is recipient plasma with donor RBC, and the result is agglutination or no agglutination: type O cells, which have no A or B antigens, into a type A recipient whose plasma has A antibodies give no agglutination and are compatible; type A cells, which have A antigens, into a type O recipient whose plasma has A and B antibodies agglutinate and are incompatible.