Mini Case B7: Case of a Disappearing Antibody

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  • Like other B level cases Case B7 focuses on basic theory and practice and is the first of a new series of mini-cases.
  • Case Study B7 deals with discrepant serologic test results in patient specimens drawn at different times during one admission.
  • The case is based on a study case used to teach students in Medical Laboratory Science at the University of Alberta in Edmonton, Alberta, Canada. It was a case experienced by the TraQ webmaster (and former MLS instructor) during her career as a medical laboratory technologist.
  • The case has been revised to reflect current practice and to include content relevant to physicians and nurses.
  • As an experiment, one of the laboratory test results has a cheat sheet refresher with an audio link.



Thanks to the following colleagues, who reviewed the case and provided valuable feedback (Their career positions are correct for when the case study was developed):

Special thanks to Christopher Ward, Medical Laboratory Science, University of Alberta, for permission to use his photographs of serologic reactions.



Mr. R.M., a 55-year old male, was admitted to a hospital emergency department with severe lower gastrointestinal bleeding. His history revealed multiple prior transfusions the last of which he received five years earlier.

Physical examination revealed hemodynamic instability (systolic BP 60 mmHg). Blood tests revealed a Hb of 80 g/L (8 g/dL) and a hematocrit of 0.28. The patient received aggressive fluid resuscitation with Ringer's lactate and was sent to the OR for an emergency laparotomy.

The physician ordered 4 units of concentrated RBC to be crossmatched as an emergency.* Two units of unmatched group O Rh negative RBC were also requested for immediate transfusion.

The transfusion service (TS) instructed clinical staff to be sure to draw crossmatch blood specimens before transfusing any blood components or products.

Blood samples were drawn and sent to the TS for pretransfusion testing. The patient was then transfused with 2 units of O Rh negative RBC. In the meantime, pretransfusion testing was in progress in the TS laboratory.

* The TS emergency crossmatch includes

  • ABO/Rh and antibody screen on the recipient

  • Electronic crossmatch for patients with a negative antibody screen and no history of prior antibodies.

  • Donor units are released once pretransfusion testing is completed.

  • The transfusion service (TS) routinely confirms the ABO of all donor units and the Rh(D) type of Rh negative donor units.





The physician was notified that compatible blood was unavailable and that the patient's antibody was still being investigated.

When asked whether or not the patient was experiencing a transfusion reaction due to the transfusion of the two unmatched and incompatible O Rh negative RBC, the physician stated that a reaction was not apparent (the patient was in the OR)but they would investigate and closely monitor.

Fortunately, the patient's condition stabilized and additional transfusions were not required.


Two weeks later, new patient specimens were drawn for antibody studies.


The patient's antibody disappeared immediately post-transfusion but reappeared two weeks later.

  1. If the patient's pretransfusion plasma was available for antibody titration, do you think the antibody titre would be lower, the same, or higher than the titre on the two-week post-transfusion specimen?


  2. What, if anything, does this case demonstrate about the risks of transfusing a patient with uncrossmatched blood? Include in your discussion an estimate of the frequency of unexpected antibodies in patients.



This case study presents a scenario in which a patient had an unexpected antibody that disappeared after he was transfused with 2 units of unmatched group O Rh negative RBC. The patient developed a positive DAT with MFA but an antibody identification using the eluate was inconclusive, making the antibody unidentifiable. Fortunately, the patient improved and further transfusion was not required. The case illustrates the risks involved in using unmatched blood.


Upon completing the case study, participants should be able to do the following:

  1. Describe possible serological test results in a patient experiencing a hemolytic transfusion reaction due to non-ABO antibodies.
  2. Explain the significance of a positive DAT with mixed field agglutination in a recently transfused patient.
  3. State the critical first steps for transfusion service staff to take when a patient is transfused with unmatched RBCs that turn out to be incompatible.
  4. Discuss the risks of transfusing unmatched RBC.



Online resources

Examples of policies for release of RBC for patients requiring emergency transfusion:

Also see