Mini-Case
Study B7:Case of a Disappearing Antibody
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Last updated:
17
Mar. 2009
NOTES
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.
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.
See
The patient's antibody disappeared immediately
post-transfusion but reappeared two weeks later.
Q. #13.
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?
Q. #14.
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.
SUMMARY
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.
LEARNING
OUTCOMES
Upon completing the case study, participants should be able to do the
following:
Describe possible serological test results
in a patient experiencing a hemolytic transfusion reaction due to non-ABO
antibodies.
Explain the significance of a positive DAT with mixed field
agglutination in a recently transfused patient.
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.
