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The same phenomenon is seen if you use a spun sample for DATs. The cells at the top can be negative and the ones from the bottom positive if recently transfused.

Thank you all so much for your explanations. I agree with jayinsat regarding the importance of transfusion history in this case, but I would have expected mixed field on the instrument, which was not the case. The concept of the density difference between the autologous RBCs vs the transfused RBCs and its impact on the probe sampling is very fascinating. Thank you all for sharing the papers that explain this phenomenon.

The most likely answer has been given above: newly formed autologous red cells have a lower gravity than transfused cells and will concentrate at the top of the re cell pellet whereas transfused cells will seat at the bottom. I hereby attach a paper describing that phenomenon. I hope Grifols will thank you for giving them the answer :-) 20230301142735376.pdf20230301142735376.pdf

I strongly suspect that you've got your answer. Echo/Lumena probes are calibrated to go to a specific depth after level sensing at the top of the plasma of the specimen and I would think that is true for other analyzers as well. Another (opposite) problem that can happen is failure to pick up a red cell sample if the Hct is extremely low. With the 'extra' plasma in the tube because of the low Hct, the probe doesn't go deep enough after level sensing the specimen to reach the red cells.

My interpretation has always been that the alarm should sound at or before the set point. The set point should be low enough to allow time to move products if necessary. But we are CAP inspected, not AABB.

Correct. That is why we typically use 5.5 as the upper set point instead of 6.0. If it alarms at 5.6, you are still covered and have time to move product before it reaches the upper limit. I think that is why I am confused by the OP's citation. I wonder if they have it set to 6.0

Well, the transfusion history was an important piece of this puzzle. I see this all the time on the ECHO Lumena. When a patient has more donor cells (group O) than autologous cells, the ECHO will often give a ? because of the mixed field reaction. When looking at the images, it looks like a clear 3+ or stronger. Tube is usually 4+ with mixed field. I should have asked transfusion history from the beginning.

We do the crossmatches if we have a sample, but there are times as applejw points out when we get no sample, so we document and move on. We supply our helicopters so keep segments from the units which we can use for serological crossmatches if needed. Mostly, we do electronic.

Well, that's got rid of two of my possible theories in one fell swoop! I was wondering either about loss of antigenicity due to some form of myeloid malignancy, or of adsorption of autologous secreted A substance on to the donor group O red cell surface following a successful BMT or stem cell transplant, which may be seen with only some clones of anti-A (see, for example, Cripps K, Mullanfiroze K, Hill A, Moss R, Kricke S. Prevalence of adsorbed A antigen onto donor-derived group O red cells in children following stem cell transplantation: A single-centre evaluation. Vox Sang 2023; 118: 153-159. DOI.10.1111/vox.13386., but I saw this phenomenon in adults many times when working at Westminster Hospital). Oh well, back to having more thoughts!

Quite concerning indeed. Luckily the mistyping is from groupA to groupO....We did contact Grifols technical support and provided all the results and lot numbers. We haven't gotten an explanation yet from their end.

Was the patient recently transfused? We had a situation several years ago where the patient sample results were one type on the Vision and another type in tube. I learned that the instrument samples red cells from the bottom of the patient specimen which, after centrifugation, is where the majority of the more dense transfused cells are vs. the top of the red cell layer where the less dense autologous red cells are. This cause for a forward typing discrepancy was confirmed after communications with Ortho. The theory was confirmed with manual gel testing where red cells were sampled from the top, middle and bottom of the red cell layer of the patient's specimen. The top layer of red cells were Group O, the middle and bottom were primarily Group A. This patient was discovered to be Group O after receiving several Group A RBC transfusions. The reverse typing showed reactivity only with Group B red cells at that time.