Antibody identification panel

Principle

• Patient plasma is tested against a panel of group O reagent red cells (typically 8–16 cells) with known antigen profiles (antigram). The pattern of reactions identifies the antibody specificity.

Specimen

• EDTA plasma or serum plus patient red cells for autocontrol, DAT and phenotyping.

Procedure

• Test plasma against each panel cell and an autocontrol using the same method and phases that detected the antibody (IS, 37 °C, AHG).
• Rule out (exclude): cross out an antigen when a panel cell carrying it gives a negative reaction, preferably using a cell homozygous for antigens that show dosage (Rh, Kidd, Duffy, MNS).
• Compare remaining unexcluded specificities with the pattern of positive cells.
• Confirm with the rule of three: at least 3 antigen-positive cells reacting and 3 antigen-negative cells not reacting (p ≤ 0.05).
• Phenotype the patient's red cells: the patient should lack the corresponding antigen (unless recently transfused).

Interpretation

• Reactions at IS or room temperature suggest IgM antibodies (anti-M, N, P1, Lea, Leb, I); reactions at AHG suggest IgG (Rh, Kell, Duffy, Kidd, S, s), which are usually clinically significant.
• Varying strength may indicate dosage or more than one antibody.
• All panel cells positive with negative autocontrol: antibody to a high-frequency antigen or multiple antibodies. Positive autocontrol: autoantibody or antibody to recently transfused cells (DAT, elution).

Quality control and pitfalls

• Enzyme-treated cells (ficin, papain) destroy M, N, Fya and Fyb (S and s variably) and enhance Rh, Kidd, Lewis, P1 and I antibodies.
• DTT treatment destroys Kell antigens and CD38, used for daratumumab interference.
• Anti-D in pregnancy may be passive from RhIG; check history.
• Kidd antibodies are often weak and cause delayed haemolytic reactions.

Clinical use

• Selecting antigen-negative red cells for transfusion, assessing HDFN risk and investigating transfusion reactions.