How are such reactions usually discovered and how do they present in the transfusion service?
The blood transfusion service discovers the majority of DHTR through serologic findings when further transfusions are ordered. Typical finding include the presence of a:
- weak (previously undetected) antibody in the antibody screen
- weak positive DAT with mixed field agglutination apparent microscopically (autocontrol, if done, would be positive in IAT phase)
- The antibody screen may be negative if, at the time of testing, the patient's antibody level is below the threshold that is detectable by the antibody detection method used.
- The antibody screen may be negative if, at the time of testing, most of the patient's antibody has been 'mopped up' (adsorbed) by the antigen-positive donor cells and excess antibody is not yet being produced. In this case, the antibody would be detected by testing an eluate made from the DAT-positive red cells.
- The DAT may be negative if most or all of the transfused cells have been destroyed when the testing is done.