Causes of a false negative antibody screen include

  • technical error (e.g., failure to add patient serum/plasma to a test)
  • clerical error (e.g., recording test results for patient A on the requisition or computer record of patient B)
  • antibody too weak to be detected by the antibody screen method
  • failure to use screen cells that are homozygous for antigens that show dosage
  • failure to use blood specimens that are less than or equal to 3 days old for pretransfusion testing
In this case,  the antibody screen was positive with homozygous screen cells but the antibody was undetectable with heterozygous red cells, including the crossmatched donor cells.

In these circumstances, crossmatch-compatible should NOT be released routinely. Because of the risks involved, they should be released ONLY in emergencies and then ONLY with the consent of the patient's physician after consulting with the director of the transfusion service or designate.

Discussion Questions

  1. Blood specimens for pretransfusion antibody screening should be no older than 3 days old. How is the "3 day rule" calculated?


  2. In this case study what is the likely reason why the patient's antibody screen was negative when the transfusion reaction investigation was done?