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Diluting QC antisera


Mindy

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We discovered at AABB that we are not meeting a CAP requirement for QC. Seems CAP requires ABSC QC to react 1-3+. We perform ABSC in gel, use 3% Ortho Surgiscreen diluted to 0.8% daily, and QC the system with Ortho Confidence system anti-sera (contains anti-D, -c). Our QC reactions are consistantly 4+. So, I've been playing around with dilutions trying to find the one that will give us a 1-3+ reaction. Unfortunately, the dilution that gives a 3+ reaction with the anti-c gives a negative reaction with anti-D.

Has anyone out there been sited by CAP for this? Does anyone out there uses this same setup? Is anyone diluting their antisera. Am I going completely mad?

Mindy

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We also use Ortho gel but we do not purchase their QC kit. We just freeze our expired antisera (duffy, kidd, etc.) and then dilute it to get 1-3+. We freeze the aliquots and get out one for the week that we keep in the fridge. It stays good and we check it when we make it to make sure we get the needed reactions. We haven't had any problems with inspection.

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Perhaps the larger question is "Why did CAP come up with this?" It stands to reason in my mind that if you're using a more sensitive test, you will get stronger reactions--and this is what you should be looking for. And, no, we couldn't get consistent results, either, with diluted Ortho QC antisera, so we've given up for the time being and just do the QC with the undiluted antisera. At least WE know the cells are ok.

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We also dilute our Ortho QC antisera for testing on Gel. We are currently diluting 1:30 and are usually getting 1+ with the D+ c- cell and 3+ with c+ cells. Our procedure includes instructions for preparing 1:20, 1:25, 1:30 and 1:40 dilutions, because some years ago the anti-D was the stronger antibody in the mix and a lower dilution worked better. This allows us to make an alternate dilution if we find that our 1:30 dilution no longer gets the expected reactions.

Interestingly, a CAP inspector/AABB assessor stated that some sites she had inspected had been using the antibody neat and had basically gotten an "exception" from CAP to do this, based on the increased sensitivity of Gel testing. I'd be interested in hearing from anyone who had made this challenge to CAP.

As an additional note, during our last FDA inspection, the investigator had some consternation that we were diluting the QC reagent, since the manufacturer's instructions for use states "do not dilute". This was in spite of the fact that we had validation to support our dilutions. After several phone calls to his superiors, he decided that what we were doing was actually "OK".

I do understand that it would be impossible to make a QC antibody that would work for every possible antibody enhancement medium. Still, it seems to me since Gel is so widely used, that Ortho should provide QC material that mets the requirements of accrediting agencies.

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We do not purchase QC reagents. Instead we just combine all of our reagents in various combinations that will cover everything. For QC of antibody screens we use diluted anti-K. We use the same dilution for testing PeG, LISS, no enhancement and gel screens. We found that there is no way to make the dilution correct so that the reactions are 1-3+ with all antibody screen methods. At this point we have made an exception for the gel method. As long as the antibody screen reactions are 1-3+ for the other three methods we are happy. Something had to give.

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  • 2 months later...

Sorry to respond to this so late but I'm new to the site and think this is a very important topic.

First, why should QC give 1-3+ and not 4+? Because when you get a 4+ reaction, all you know is that you will detect strong reactions. You don't know if your system (reagents + method + equipment + staff) will detect weak reactions as are often seen in patient testing.

Second, regarding dilution of reagents for QC - be careful! Reagent manufacturers add things to their reagents to make them avid (give strong results) and stable. If you dilute them too much, you can make them very unstable. I always recommend that if you are going to dilute reagents you should use saline with some amount of bovine albumin (3-6%) in it.

Lastly, if you can't make QC work, it might not be a problem with the reagents - it might be a problem with your system and the QC is telling you EXACTLY what you need to know, i.e., maybe you're doing something wrong.

This might make me wildly unpopular, but please at least think about it.

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We purchase a liquid plasma from our blood center that contains weak (1+ to 2+) alloantibodies. We aliquot this plasma into 25 ml aliquots and freeze them. We thaw as needed. One unit of plasma is good for at least two months of QC. This works for both gel QC and tube QC, no dilution needed. Rare antisera, even the outdated sera, is too expensive to use for QC!

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