Tag: ABO discrepancy

“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.

-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.

I have taught Transfusion Medicine to MLS students for a number of years, and one of the more challenging concepts for my students is that of ABO discrepancies. We use ‘dry’ labs for ABO discrepancy examples because it would be difficult to create actual samples that illustrate the various scenarios. Without seeing this in the lab, and actually performing the steps to resolve, visual learners in particular can be at a disadvantage. In reality, some of the more unusual ABO discrepancy problems are found more often on exams than in real life. Consequently, in the Blood Bank lab, when a technologist comes upon an ABO discrepancy, it can be something they are not very experienced with and it can be more scary than exciting. I have always felt that one of the best things about being a medical technologist is that we get to solve puzzles and find answers. So, let’s put on our detective hats and follow along with our case history story of an ABO typing discrepancy.

Once upon a discrepancy… a forward typing did not match a back typing. The first thing the tech did was to repeat the typing. Many labs recommend using a different method in the repeat, so if typings are routinely done by an automated method, a repeat testing might be done by tube typing. In this case, we can see the results of the initial testing and the results of the tube typing below:

Automated typing

Reagent	Anti-A	Anti-B	Anti-D	A1 Cells	B Cells	Interpretation
Results	4+	0	4+	1+	3+	??

Repeat tube typing

Reagent	Anti-A	Anti-B	Anti-D	D Control	A1 Cells	B Cells	Interpretation
Results	4+	0	4+	NT	1+	4+	??

 

As you can see, the repeat typing simply rules out technical or clerical errors and confirmed that the testing was performed correctly. So far so good. However, since we got the same results on repeat testing, what is the next step in resolving this discrepancy?

I teach my students to think of a few ground rules when working on ABO discrepancy problems. The first is that, typically in these situations, it is the weak reaction that is the discrepant one. We have a patient who front types as an A, but the back type looks like an O. With ABO typing we usually get fairly strong reactions, so the 1+ reaction with A1 Cells is the suspect one. The second rule of thumb is that antibody problems are much more common than antigen problems. Having and extra antibody reaction or missing an antibody reaction is more common than extra or missing antigens. In this case we have an extra antibody reaction. This patient looks like a group A who is making anti-A1 which has reacted with our A1 cells.

Our next step is to discover why we have an extra antibody. I would like to emphasize the importance of looking up the patient’s history to help you resolve a discrepancy. This is the third thing that should always be done when investigating an ABO discrepancy. Accurate patient history including any previous Blood Bank results, age, pregnancy history, medications and diagnosis can all be used to help resolve these problems.

At this point techs are probably thinking ‘This is easy!’ and thinking about A subgroups. Remember that about 80% of group A people are group A1 and about 20% are group A2. There are also other less common subgroups of A, but A2 is the one that we encounter most often. Some group A2 people can make anti-A1, either naturally or as an immune response. This patient is a 30 year old woman who is in the Emergency Room and has just been scheduled for surgery. The physician has ordered a type and crossmatch for 2 units of blood. A look at her medical history shows she has never been pregnant nor has ever received blood products. We have no previous Blood bank history on the patient. While an anti-A1 can be from previous transfusions or pregnancy, it can also be naturally occurring. This seems to support our speculation that she is an A2 subgroup with a naturally occurring anti A1, so while we are waiting for our screen results, we perform A1 lectin testing. The results are shown below:

If our patient was group A2 as we thought, her A2 cells would not react with anti-A1 and her plasma would not have anti-A2 and would not react with A2 cells. Our results do not match our original hypothesis that the patient is group A2 and we can rule out a subgroup of A. What is her type, and what is causing the discrepancy?

To help solve this discrepancy, the tech looked at the solid phase screening results only to find that the screen was negative, thus making this puzzle even more perplexing. He repeated the screen in tube at IS, 37C and AHG and found positive reactions. Working up the panel, Anti-M was identified!

So, what type is this patient? She is group A1 pos with an cold reacting anti-M antibody. The policies of the medical center would determine if this patient should be given cross match compatible units that are not antigen typed or crossmatch compatible M negative units.

Anti-M is a naturally occurring cold antibody. Most examples of Anti-M are IgM, do not react at 37C and are not considered to be clinically significant. However, anti M can also present with an IgG component and react at 37C and AHG. In this case, it would be considered clinically significant and any units transfused must be negative for the M antigen.

This patient’s anti-M was only reacting at IS and determined to be not clinically significant. Despite this, we have seen that non-ABO alloantibodies can and do interfere with ABO typing and are a common cause of unexpected reactivity in ABO reverse typing. Performing the ABO testing at warm temperatures or repeating the reverse grouping with reagent A1 and B cells that are negative for M antigen can eliminate the cold reactivity and help resolve the discrepancy. It is important to remember that we must not only recognize discrepant results, but also resolve them adequately. Correct blood typing of patients is essential to prevent ABO incompatible transfusions and to help prevent alloimmunization.

References

1. http://www.haabb.org/images/14_Hamilton-Neg_Ab_screen_For_website.pdf
2. Harmening, Denise M. Modern Blood banking and Transfusion Practices, 6th Ed. 2012
3. Safoorah Khalid, Roelyn Dates, et al. Naturally occurring anti M complicating ABO grouping. Indian Journal of Pathology and Microbiology. Vol 54, Issue 1, 2011. P 170-172

 

-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.