Patient history can provide valuable information when trying to identify an antibody. For example, some antibodies are associated with a particular race or ethnicity. Transfusion or pregnancy history are helpful to determine if the antibody is naturally occurring or immune.
The antibody screen can provide sufficient data to make initial hypotheses regarding the likely antibody specificities and may be useful to presumptively rule-out some antibody specificities. When analyzing the antibody screen data, the strength/characteristics of reactions (for example, mixed-field or weak versus strong), the phase of testing (for example, room temperature versus AHG), and the pattern of reactivity (which cells react and which do not) are all important factors that will provide clues about the possible identification of the antibody(ies). Many antibodies exhibit dosage, that is, they react more strongly with homozygous cells than with heterozygous cells.
If a tube method is used, reactions can be read at immediate spin, 37°C and AHG phase. Most facilities will only perform agglutination readings at AHG for routine antibody screening. If a gel method is used, reaction readings are always only done at AHG phase.
- Reactions occurring only at immediate spin phase could indicate a possible IgM antibody, cold agglutinin, or rouleaux.
- Reactions occurring in the 37°C and AHG phase could indicate a possible IgG antibody.
- Reactions occurring in both reaction phases could indicate a combination of both IgM and IgG antibodies or a strong IgM antibody that carries through to AHG phase.
The presence of multiple antibodies should be considered if reactions vary in strength or there are two separate reaction patterns in the IS and AHG phases.