There are two potential problems in typing a recently transfused patient who develops a positive DAT:
- There will be two cell populations, patient and donor red blood cells.
- If the typing sera reacts by IAT, the positive DAT will cause false positives.
In the case presented, the DAT has become negative. This also suggests that most (if not all) transfused donor red cells have been removed from the patient's circulation.
Regardless, to be on the safe side, the patient's initial pretransfusion specimen, which was DAT negative and consisted of only the patient's red blood cells, should be used for antigen phenotyping.