A Tale of Two Types

“It was the best of times, it was the worst of times.” In the blood bank, some of the best days can come from some of the worst days. When we come together as a team to work on a puzzling antibody problem, or to respond to a trauma, we can take pride in our work and know we have done our best to help the patient. In the blood bank we are constantly being called upon to learn and to be “disease detectives.” These are the best times. I tell my students that antibody panels are like puzzles and ABO discrepancies are mysteries to solve. Of course, when the Emergency Room is calling for blood for a trauma, or the Operating Room has an emergency surgery on a patient not previously type and crossed, any “problem” to solve can be a bit stressful.

ABO discrepancies are one challenge we face in blood banking. These are generally not clinical problems, but are serologic problems encountered by the blood bank technologists. Some discrepancies are easier to resolve than others, but still usually require a bit of investigation, and time. We don’t see these every day, so they can set us back a step when we do come across them.

One such situation that I recall was a young man in the ER who arrived by ambulance after a motor cycle accident. My trauma beeper went off and I called the ER to see if they wanted blood right away. Typically in these cases we bring them O blood in a cooler, and continue to use type O until we have a blood sample and current type, (performed twice if no prior history) and an antibody screen. In this case we were fortunate in that we got a sample almost immediately, before they started any transfusions. The type and screen was put on our Provue, but the instrument flagged an error on the type. When looking at the gel card, I could see mixed field reactions. Serology results are shown.

Anti-A Anti-B Anti-D Rh cont A cells B cells ABO/Rh
2+mf 0 2+ 0 0 4+ ?

ABO discrepancies occur when unexpected reactions occur in the forward or reverse grouping or the forward typing does not match the reverse typing. In general, RBC and serum grouping reactions are very strong; therefore reactions less than 3+ usually represent the discrepancy. In this case, testing patient cells with anti-A gave a 2+ mixed field reaction and patient cells and anti-D was only a 2+ reaction. The first step was repeating the test with the same sample. The repeat tube typing gave the same results. Additional steps included testing a new sample, completing the antibody screen, which was negative, and reviewing the patient history. At this time, we did have a positive identification on the patient and a medical record number. The patient had no previous Blood Bank history. However, reviewing the ER admission notes, it was noted that the patient had received 2 units of O negative packed cells in the ambulance en route to the hospital. Viewing the anti-A and the anti-D tubes under the microscope confirmed presence of mixed field agglutination.

Mixed field agglutination describes the presence of two populations of red cells. Mixed field agglutination is seen as small or large agglutinates in a field of many unagglutinated cells. In this case, we observed mixed field agglutination with the patient’s own circulating type A positive red blood cells agglutinating with the anti-A antisera, and the type O donor cells he received remaining unagglutinated. Patients can show mixed field reactions after recent out of group transfusions of as few as 1 or 2 units of packed cells. As well, when group O packed RBCs are transfused to a group A, B or AB recipient, there is always a small amount of plasma transfused. Thus, anti-A, anti-B and anti-A,B are almost always passively transferred. Even though it is unlikely that the passively acquired ABO antibodies will cause in vivo hemolysis, it would be recommended to continue transfusing O blood instead of type specific blood for the duration of the immediate episode and until anti-A antibodies are no longer detectable in the patient’s serum.

This case is an example of an artificial chimerism. Chimerism is the presence of 2 cell populations in a single individual and, in this case, was easily explained by the recent out of group transfusions.  This patient was sent to surgery and continued receiving several more units of group O RBCs during and after surgery. The patient’s blood type continued to appear as a mixed cell population during his hospital admission.

There are a number of other scenarios in which mixed field reactions could cause a discrepancy in a patient’s ABO/Rh typing. Some weak subgroups of A (A3) are known for giving mixed field reactions. Mixed field reactions can also be seen in other artificial chimera cases, such as are seen with transplanted bone marrow or peripheral blood stem cells of a different blood type.  If mixed field reactions are present, review the patient’s transfusion history to determine if the patient has been transfused with non-group specific RBC components in the past 3 months or received an ABO-mismatched stem cell or bone marrow transplant. More uncommon and unusual are cases of true chimerism, which can occur with fraternal twins.  Stay tuned for my next transfusion medicine blog for a discussion of chimerism!

A few key tips to remember when encountering an ABO discrepancy:

  • Retest the sample first, using a different method, if available
  • Check for technical or clerical errors
  • Remember that the weakest reactions are usually the ones that are in doubt
  • Complete the antibody screen and note positive reactions
  • Check the patient diagnosis
  • Check Blood Bank history
  • Most of all, take a deep breath and relax. You can solve this!

References

  1. Charles Dickens. A Tale of Two Cities. 1859
  2. George Garratty. Problems Associated With Passively Transfused Blood Group Alloantibodies. AJCP, June 1998
  3. Denise M. Harmening, Modern Blood banking and Transfusion Practices, Sixth edition, 2012.
  4. Christopher Sharpe, et al. Mixed field reactions in ABO and Rh typing chimerism likely resulting from twin haematopoiesis. Blood Transfus. 2014 Oct; 12(4): 608–610.

Socha-small

-Becky Socha, MS, MLS(ASCP)CM BB CM graduated from Merrimack College in N. Andover, Massachusetts with a BS in Medical Technology and completed her MS in Clinical Laboratory Sciences at the University of Massachusetts, Lowell. She has worked as a Medical Technologist for over 30 years. She’s worked in all areas of the clinical laboratory, but has a special interest in Hematology and Blood Banking. When she’s not busy being a mad scientist, she can be found outside riding her bicycle.

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