Situation - RBC and plasma issued emergently to patient. 2 units RBC and 2 units plasma transfused in ER.  Testing on patient specimen drawn pre-transfusion showed 2+ reactivity with screening cells and anti-K1 was identified.  When performing compatibility testing, the 2 transfused RBC were compatible when tested on the Vision using a 2nd specimen collected after the original specimen used to perform Type and antibody screen (insufficient plasma remaining from pre-transfusion specimen to perform any additional testing).  After performing antigen testing on all units, unit #1 was tested as K1 positive and unit #2 was K1 negative.  Compatibility testing using manual gel technique was performed on unit #1 to verify the negative test result - but was found to be 2+ incompatible. This testing was performed using a 3rd specimen collected at the same time the initial specimen was collected (CBC specimen obtained from Hematology).  This was repeated on the same Vision instrument and was 2+ incompatible using the CBC specimen.

Is it reasonable to assume that the plasma transfusion (along with associated IV fluids used in resuscitation) would have diluted the existing antibody enough to yield negative test results with an incompatible RBC unit?

If the antibody was weak, it could be that there was a combination of a dilution effect from the plasma transfusion and associated IV fluids, but also adsorption of the weak and diluted antibody in vivo by the unit that was K Positive.  If the patient has survived the trauma that brought him/her into the ER in the first place,you can probably expect a bounce back in titre within a couple of days, as the "excess" liquid will be excreted, and the immune system will "gear up" after the boost given by the K Positive unit.  Mind you, sometimes, if the patient is bleeding profusely, the immune system seems to "shut down", in terms of being boosted.

I initially thought that some of the antibody would be adsorbed onto the transfused positive cells but wasn't sure if that would be enough to completely remove the reactivity - but apparently it sure helps!

Some one has to ask so I guess I will.  How confident are you that the 2nd sample actually came from this patient?  I know it is unlikely but unlikely is not impossible, hence my question.  Just a thought to consider.    

Bye the way, I agree with Malcolm's assessment.

My initial answer would be no.  Haven't seen this happen with a transfusion of 1 unit.    Would have to recheck the whole process of the 1st sample (pre transfusion), starting from the collection (correct patient, correct collection site, correct person collecting, correct labeling, specimen handling, specimen testing, etc.etc)….  maybe there was an error along that path and not a immunohematological issue?

15 minutes ago, mrmic said:

My initial answer would be no.  Haven't seen this happen with a transfusion of 1 unit.    Would have to recheck the whole process of the 1st sample (pre transfusion), starting from the collection (correct patient, correct collection site, correct person collecting, correct labeling, specimen handling, specimen testing, etc.etc)….  maybe there was an error along that path and not a immunohematological issue?

I assumed the clerical side of things had already been checked.

So, this patient was initially seen as a trauma with an unidentified "identifier".  The 2nd sample labeling was verified (by several people including myself) - collected at a different time according to the label. Patient's initial sample was B POS and this sample was also B POS.  It is always possible that the second sample was collected from a different trauma patient in the ER that was also B POS around the same time but, because of the probability of another B POS patient in the same vicinity in the same time period, I don't believe that is the cause but cannot exclude this possibility.  The hematology sample was also B POS. I did check other trauma samples received during that time and there were no other samples tested as B POS.

Ok, I'll ask the other question that needs to be asked:  Are you SURE that the cells put into the vial for Unit #1 are from Unit#1? 

Serologically, those discrepant results don't make sense (which is why you are inquiring) so I'm looking at the mechanical issues.  Is it possible that during the heat of the moment (STAT, Uncrossmatched), the tech who retrieved the segments from the 2 units actually pulled both segments from Unit #2?  When the crossmatches were repeated manually, was a new segment taken from the unit and that's why you saw the expected incompatibility?

Repeat testing used the cells that were originally placed on the Vision for compatibility testing .  These were incompatible using the lavender-top tube but compatible when tested with the 2nd pink top.  I think that, whatever the cause , the answer is found with the 2nd pink top tube.  Two possible scenarios:

1)  2nd pink top collected from a different patient who coincidentally was also B POS and in the ER around the same time

2) Antibody titer decreased due to transfusion or dilution.

At this point, it is a conundrum and might be academic but an interesting story.  Thank you, everyone, for your thoughts!

Is it possible that a sample was drawn in a different tube/additive then poured into the pink top?

1.  did you think to do a DAT on the posttransfusion sample to see if the antibody was all 'stuck' on to the transfused red cells?

2.  What method did you use to K-type the units of blood?  did it involve an IAT?  If so was the positive result a false positive because the unit had a positive DAT?