Patients with WAIHA present with very difficult serological problems such as blood typing discrepancies, strong positive results in antibody screens, incompatible crossmatches, positive direct antiglobulin tests (DAT), or antibody panels/eluates reactive with all cells.
A positive DAT is expected in WAIHA. The patient's serum may contain little free autoantibody if the autoantibody has been primarily adsorbed by the red cells in vivo. Autoantibody will appear in the serum once all the antigen sites on the red cells have been occupied. In the majority of cases of WAIHA, the DAT is positive with both IgG and complement. In approximately 20% of cases, the DAT is positive with IgG alone and in a few cases, the DAT is positive with complement alone.
About half of all WAIHA cases will have an autoantibody that reacts with all cells tested, including donor cells. The presence of an IgG autoantibody can be confirmed by elution. Elution is the process by which RBC-bound antibody is removed from the red cells and recovered, being sure that antibody reactivity is maintained so that antibody specificity can be determined. The eluate is usually reactive with all cells tested. Most IgG autoantibodies have an Rh-like specificity, such as anti-e. In order to identify the specific antibody, the laboratory would need to have a supply of rare cells such as Rhnull and D-- cells. Other specificities include those to high incidence antigens or a null phenotype. Examples include autoanti-U, autoanti-Wrb, autoanti-Ena, autoanti-Kpb, and autoanti-Vel.
However, it is rarely necessary to perform extensive additional testing to determine the autoantibody specificity. The specificity is usually only of academic interest. The detection and identification of alloantibodies should be the primary concern.