Antibody detection and identification are performed by testing patient serum or plasma with reagent red cells. Agglutination or hemolysis indicates sensitization of the reagent red cells by an unexpected antibody in the patient's serum. The reagent red cells come with an antigram or antigen profile sheet. The antigram shows the phenotype of each reagent cell used.
Antibody detection is performed using an antibody screening test. An antibody screen consists of 2 or 3 group O reagent red cells with known antigen phenotypes. A positive antibody screen means that an unexpected antibody is present in the patient's serum.
If the antibody screen is positive, the antibody must be identified by performing an antibody panel. A panel consists of 10 to 20 group O reagent red cells with known phenotypes.
The image below depicts an antibody screening antigram. A "+" indicates the antigen is present on the cell and a "0" indicates the antigen is absent. The antigram will also tell us if a cell is homozygous or heterozygous for an antigen. Looking at the Kidd blood group system, cell 1 is heterozygous (Jka+ Jkb+) while cell 2 is homozygous (Jka+ Jkb-).