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Positive Antibody screen but negative antibody ID panel

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Posted (edited)

Can anyone tell me what is going on here and why?

Okay, I got a type and screen ordered on a specimen. We did the type , and the patient was A Pos. The antibody screen was positive.  Then we did an antibody identification panel, it was all negative, including the auto-control it was also negative.  All typing, Ab screen, Ab panel, and auto-control was performed by gel cards.

 

What is going on here and how can we solve it? Thank you.

 

Edited by diplomatic_scarf

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It sounds remarkably like one of your screening cells is expressing a low prevalence antigen that is not expressed on your panel cells.

Antibodies directed against low prevalence antigens are actually quite common, but they are rarely detected because red cells expressing the cognate antigen are so rare.

I wouldn't expend too much time or energy trying to sort out the exact specificity.  In all cases of such an antibody, as long as you cross-match by the same method as you used in detecting the presence of the antibody in the first place, it would be quite safe to give cross-match compatible blood.

The other thing is that the screening cell may be expressing an HLA antigen.  You could treat the cell with chloroquine, and that will get rid of the HLA antigen.

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In addition to what has been nicely explained by Malcolm, it could be as well an example of Sd(a++) cell (commonly named "super Sid") reacting with a weak anti-Sda. The Sda antigen is not a LFA (expressed on more than 90% of cells) though some cells "overexpresse" it.

Anti-Sda usually gives weak/DP reactions and can be neutralized using urine (contains soluble Sda substances). 

Other weak antibodies may behave the same way, e.g. anti-P1 reacting against "strong P1" cells only.

However, that does not change at all what Malcolm said "I wouldn't expend too much time or energy trying to sort out the exact specificity.  In all cases of such an antibody, as long as you cross-match by the same method as you used in detecting the presence of the antibody in the first place, it would be quite safe to give cross-match compatible blood."

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Posted (edited)

I'd parrot the same sentiments listed above. As long as you have ruled-out all other clinically significant antibodies, call the identification a low frequency and call it a day. You'll have to perform any future crossmatches with the same methodology. The chances of it being some crazy rare antibody is, of course, low.

There was also another thread listed here with a similar question.

Edited by Ward_X
addition

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This is a long shot, but if your patient is black and transfused often, it could be ant-Jsa or anti-V/VS.  We see that not infrequently with our sickle cell patients who are on a chronic transfusion protocol. 

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Posted (edited)
47 minutes ago, Baby Banker said:

This is a long shot, but if your patient is black and transfused often, it could be ant-Jsa or anti-V/VS.  We see that not infrequently with our sickle cell patients who are on a chronic transfusion protocol. 

It is a long shot.  I don't think I've ever seen a Jsa+ screening cell.

Plus - it would be nice to know how strong the reaction(s) was and which cell(s) was reacting.

Edited by David Saikin
more thought

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It does occur, but what we see more often is a negative screen and about a quarter to a third of the units incompatable by Coombs crossmatch.  These patients get transfused about once a month, so we still do AHG crossmatches on them.

 

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On 4/17/2020 at 5:55 AM, Malcolm Needs said:

It sounds remarkably like one of your screening cells is expressing a low prevalence antigen that is not expressed on your panel cells.

Antibodies directed against low prevalence antigens are actually quite common, but they are rarely detected because red cells expressing the cognate antigen are so rare.

I wouldn't expend too much time or energy trying to sort out the exact specificity.  In all cases of such an antibody, as long as you cross-match by the same method as you used in detecting the presence of the antibody in the first place, it would be quite safe to give cross-match compatible blood.

The other thing is that the screening cell may be expressing an HLA antigen.  You could treat the cell with chloroquine, and that will get rid of the HLA antigen.

Thank you for replying.  Everything was done by gel card, we don't use the tube method.  Patient was typed A Pos. The antibody screen was 1+ positive on Screening cell 1 and 3, negative on Screening cell 2.  But when we did the Antibody Identification panel and Auto control , they were all negative. We repeated everything and got the same results.  We redrew the patient for a new specimen and got the same results. 

We sent out the specimen for an Antibody Identification at a reference lab. The result we got back was Anti-M. 

I am just wondering, why didn't our panels picked this up? Why only the screening cells were positive? What was the reasoning behind this? The panel and all our reagents have passed QC and are not expired. There was no signs of contamination in our specimen or reagents. Thank you. 

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On 4/17/2020 at 6:46 AM, exlimey said:

All screening cells reactive, or some other pattern ?

Thank you for replying.  Everything was done by gel card, we don't use the tube method.  Patient was typed A Pos. The antibody screen was 1+ positive on Screening cell 1 and 3, negative on Screening cell 2.  But when we did the Antibody Identification panel and Auto control , they were all negative. We repeated everything and got the same results.  We redrew the patient for a new specimen and got the same results. 

We sent out the specimen for an Antibody Identification at a reference lab. The result we got back was Anti-M. 

I am just wondering, why didn't our panels picked this up? Why only the screening cells were positive? What was the reasoning behind this? The panel and all our reagents have passed QC and are not expired. There was no signs of contamination in our specimen or reagents. Thank you. 

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On 4/17/2020 at 8:08 AM, John C. Staley said:

I'm with exlimey, please clarify what you mean by positive antibody screen.  One cell positive or all cells positive or something in between.

 :coffeecup:

Thank you for replying.  Everything was done by gel card, we don't use the tube method.  Patient was typed A Pos. The antibody screen was 1+ positive on Screening cell 1 and 3, negative on Screening cell 2.  But when we did the Antibody Identification panel and Auto control , they were all negative. We repeated everything and got the same results.  We redrew the patient for a new specimen and got the same results. 

We sent out the specimen for an Antibody Identification at a reference lab. The result we got back was Anti-M. 

I am just wondering, why didn't our panels picked this up? Why only the screening cells were positive? What was the reasoning behind this? The panel and all our reagents have passed QC and are not expired. There was no signs of contamination in our specimen or reagents. Thank you. 

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On 4/17/2020 at 9:20 AM, David Saikin said:

It is a long shot.  I don't think I've ever seen a Jsa+ screening cell.

Plus - it would be nice to know how strong the reaction(s) was and which cell(s) was reacting.

Thank you for replying.  Everything was done by gel card, we don't use the tube method.  Patient was typed A Pos. The antibody screen was 1+ positive on Screening cell 1 and 3, negative on Screening cell 2.  But when we did the Antibody Identification panel and Auto control , they were all negative. We repeated everything and got the same results.  We redrew the patient for a new specimen and got the same results. 

We sent out the specimen for an Antibody Identification at a reference lab. The result we got back was Anti-M. 

I am just wondering, why didn't our panels picked this up? Why only the screening cells were positive? What was the reasoning behind this? The panel and all our reagents have passed QC and are not expired. There was no signs of contamination in our specimen or reagents. Thank you. 

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On 4/17/2020 at 7:45 AM, Arno said:

In addition to what has been nicely explained by Malcolm, it could be as well an example of Sd(a++) cell (commonly named "super Sid") reacting with a weak anti-Sda. The Sda antigen is not a LFA (expressed on more than 90% of cells) though some cells "overexpresse" it.

Anti-Sda usually gives weak/DP reactions and can be neutralized using urine (contains soluble Sda substances). 

Other weak antibodies may behave the same way, e.g. anti-P1 reacting against "strong P1" cells only.

However, that does not change at all what Malcolm said "I wouldn't expend too much time or energy trying to sort out the exact specificity.  In all cases of such an antibody, as long as you cross-match by the same method as you used in detecting the presence of the antibody in the first place, it would be quite safe to give cross-match compatible blood."

 

Thank you for replying.  Everything was done by gel card, we don't use the tube method.  Patient was typed A Pos. The antibody screen was 1+ positive on Screening cell 1 and 3, negative on Screening cell 2.  But when we did the Antibody Identification panel and Auto control , they were all negative. We repeated everything and got the same results.  We redrew the patient for a new specimen and got the same results. 

We sent out the specimen for an Antibody Identification at a reference lab. The result we got back was Anti-M. 

I am just wondering, why didn't our panels picked this up? Why only the screening cells were positive? What was the reasoning behind this? The panel and all our reagents have passed QC and are not expired. There was no signs of contamination in our specimen or reagents. Thank you. 

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39 minutes ago, diplomatic_scarf said:

Thank you for replying.  Everything was done by gel card, we don't use the tube method.  Patient was typed A Pos. The antibody screen was 1+ positive on Screening cell 1 and 3, negative on Screening cell 2.  But when we did the Antibody Identification panel and Auto control , they were all negative. We repeated everything and got the same results.  We redrew the patient for a new specimen and got the same results. 

We sent out the specimen for an Antibody Identification at a reference lab. The result we got back was Anti-M. 

I am just wondering, why didn't our panels picked this up? Why only the screening cells were positive? What was the reasoning behind this? The panel and all our reagents have passed QC and are not expired. There was no signs of contamination in our specimen or reagents. Thank you. 

Reactivity with two of three cells effectively rules out the "antibody to a low incidence antigen" argument.

Is the supplier/manufacturer of the Screening Cells the same as the supplier/manufacturer of the panel ? If not, then I suspect formulation differences of the two products may be the answer, specifically pH of testing environment. 

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Yes indeed different pH, different suppliers may explain such a behavior (some anti-M are enhanced with acidification of plasma).

In addition, Anti-M often shows dosage effect but I believe you have antigen M double dose cells on your panel too. 

What are the phenotype of the 2 cells reacting in screening and the one not reacting? Is your patient antigen M negative?   

It also exists the anti-M1 (the M1 antigen belongs to the MN CHO collection) that reacts with some M positive cells and stronger with M/N positive cells (M1 is expressed on M positive cells) and it can be, though rarely, produced by antigen M positive patients.    

 

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