Ortho Clinical Diagnostics 0.8% Panel A, lot # VRA215 exp 2/17/15, cell #6:

 

We have had 2 examples of anti-M that react with all double- and single-dose cells except cell #6.  Cell 6 is M+N+, and it DOES react with commercial anti-M.   One of these examples was reacting at a strong 3+ with all other single-dose cells on the panel.  I called our reference lab, and they suggested that maybe there is a low-prevalence antigen on the cell causing steric hindrance.  I noticed that the cell is also Le(a-b-), so maybe this is a cell from a black donor, and is more likely to have one of these pesky low prevalence antigens from the MN CHO collection.  Any thoughts?

 

Has anyone else noticed this?  If so have you contacted Ortho? 

Edited February 8, 201510 yr by Whitney Poplin

Thanks Whitney for posting this question!  I do not have an answer, but your question is an opportunity for me to learn. 

 

I was wondering how low prevalence antigens from the MN CHO collection would cause steric hindrance.  After reviewing information in The Antigen Fact Book, I am reminded that the MNS antigens are on GPA and GPB which are single-pass membrane sialoglycoproteins.   One of the major functions of sialoglycoproteins is to contribute to the negative charge of the RBC glycocalyx.

 

The antigens in the MN CHO blood Group Collection, which are more frequently found in Blacks, are also on GPA and GPA and have altered sialic acid. 

 

So, if cell #6 of this Ortho panel has one of these low incidence antigens, there is a stronger negative charge and this stronger charge is weakening the anti-M/M antigen reaction?  Is that correct?  Wow--that would never have occurred to me.

 

I hope you get an answer!  A call to Ortho seems to be in order!

 

And, I hope I do not change the course of this thread too much when I ask if others have seen cases where steric hindrance has caused negative reactions when a positive reaction would be reasonable.

 

Catherine Baldwin CLS, MT(ASCP)SBB^cm

Edited February 11, 201510 yr by cbaldwin

Well, it could be that your cell has become contaminated in some way.  Or that the cell is M1+ rather than M+.  Or it could be that the cell just has fewer M antigens than some of the other heteros on the panel......how strongly are the other MN cells reacting?

One patient example of anti-M is reacting strong 3+ with all of the other single-dose cells on the panel.  This cell #6 is also a single-dose cell.  There was no evidence of contamination; i.e. no hemolysis or discoloration of the reagent.  If there was bacterial contamination and therefore a bacterial deacetylase that possibly removed NeuAc (sialic acid) off of GPA, wouldn't the cell also become polyagglutinable?  I can't remember if that process actually alters the M antigen.  This cell was not reacting at immediate spin with the patient's sample, either, as it was with the other reagent cells.  

I converted cell 6 along with 2 other single-dose cells to 3% and tested all 3 against commercial anti-M, and they all reacted equally at 2+.  I would have to check the package insert to see if M1+ cells react with the commercial anti-M; however if I remember right, M1+ cells are almost if not always M+ as well.  Is there was a situation where the M antigen would be altered or have a decreased expression that would react with commercial anti-M but not patient anti-M?  Anyone?

Or maybe I should say, if there was bacterial contamination sufficient enough to alter the M antigen, would this not also make the cell polyagglutinable?