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We are considering changing the way we "QC" a titer.

What we currently do is perform a titer, then freeze an aliquot of the plasma.  The next time we titer that patient, we thaw the original titer and perform it in parallel with the new titer.  The prior titer and the retested prior titer must agree within one dilution of each other.

What if the first titer was not done correctly, then the repeat should not match?

We are considering titering a donor who tests positive, maybe have a panel of people titer it to determines its result, then freeze small aliquots of that to be used as a control.

What are others doing?

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You are quite correct in asking, "what if the original titre was performed incorrectly?", but you have to draw the line somewhere.

If you are performing the titre of an anti-Jka, you would (I hope) use a red cell sample that types as Jk(a+b+)?  From the text books, you would assume that the red cells express 7, 000 Jka antigens per red cell (given that there are, on average 14, 000 Kidd antigen sites per red cell), but, this is an estimation in itself, and is also the average of the various experiments performed to find out the number of Kidd antigens per red cell.  It follows that, unless you use exactly the same source of red cells each time you are performing the anti-Jka titration, you cannot guarantee that the titre of the QC will be within one dilution of the previous result.

The same applies for, for example, ABO titres, where the number of antigen sites differs from one individual to another, but also from the age of the various individuals.  The adult A1 red cell has between 810 000 and 1 170 000 antigen sites per red cell.  The red cells of a new-born will only carry between 250 000 and 370 000 copies of the A1 antigen.   Now, I am not suggesting for a single minute that you would use the red cells of a new-born, but there is still quite a difference between an adult with just over 800, 000 A1 sites per red cell, and almost 1, 200, 000 sites per red cell.

As long as such a situation is an unusual occurrence, and not a regular occurrence, I wouldn't worry.

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Are there reagents currently used for Bench QC that could also be used in these cases? A set, pre-made vial that could be validated and tested (perhaps, yes, by a "panel" of people... or perhaps made by one tech, validated by another, or two)? A diluted anti-K, perhaps? Perhaps you could do this colorimetrically. Have a premade set of tittered out tubes with colored dye and a chart, and the check has to be between a certain hue/degree listed on the chart? Not sure if that is too complicated...

It's unfortunate to even consider the first testing was performed incorrectly, but if it's a recurrent issue, it could also come down to training -- are people pipetting correctly? going to the first stop or second stop of the pipette? How dramatic are these discrepancies in reading -- is it between an M and 2? Or, does this actually come down to needing to verify/QC the performance of a titer?

No two techs will ever pick up the exact same population of cells, no. But I'm sure you could find a standard practice to work for a few weeks at a time, or something along that lines to verify titers are legit.

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Posted (edited)

I may be mistaken, but I think the idea behind freezing an initial specimen that was titred and then thawing and running in parallel with subsequent titres, was so that if there is any variation in technique between one testing event and another, the retest of the initial specimen along with testing the subsequent specimen would eliminate any question as to how the titres have risen (or not)--in comparison to each other as they are being tested at the same time--when the subsequent specimen is received and tested,

Scott

 

Edited by SMILLER

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2 hours ago, SMILLER said:

I may be mistaken, but I think the idea behind freezing an initial specimen that was titred and then thawing and running in parallel with subsequent titres, was so that if there is any variation in technique between one testing event and another, the retest of the initial specimen along with testing the subsequent specimen would eliminate any question as to how the titres have risen (or not)--in comparison to each other as they are being tested at the same time--when the subsequent specimen is received and tested,

Scott

 

I agree entire;y Scott, but some people think that the frozen sample has to be "identical" in terms of a titre, otherwise the new titration is unacceptable (I know, I know)!

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On ‎8‎/‎27‎/‎2019 at 6:18 AM, SMILLER said:

I just read what I posted yesterday and would like to officially submit that post for longest sentence of the month.

Scott

Can we call you Scott "Charles Dickens" Miller?

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