There are 2 potential problems in typing a recently transfused patient who develops a positive DAT:

  1. There will be 2 cell populations, patient and donor rbc.
  2. If the typing sera reacts by IAT, the positive DAT will cause false positives.

In this case, the DAT has become negative. This also suggests that most transfused donor RBC have been removed from the patient's circulation.

  • Regardless, to be on the safe side you should use the patient's initial pretransfusion specimen, which was DAT negative and consisted of only the patient's rbc.