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The following message was posted to: PharmPK
Just curious. If you were told that an assay did not give reproducible
results when frozen qc were measured against fresh calibrators but that
the calibrator had to be frozen to get agreement would you have any
issues?
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The following message was posted to: PharmPK
I would. Something is going on. While I don't know the details, my first
thought would on stability but other physiochemical issues may be in play.
One of the more exotic is the "hard apple cider effect" (called "Jacking",
see http://www.instructables.com/answers/how-do-you-make-hard-cider/),
where in partially defrosted QCs, the center is still frozen and is enriched
with analyte, leaving concentrations in the thawed part artificially lower.
This would be fixed by proper thawing and mixing.
Christopher J. Kemper, Ph.D.
Pharma Navigators, LLC
DMPK/Bioanalytical Consulting
Alliance Management/Business Analysis
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Dear Ed-
Regarding an assay that did not give reproducible results when frozen
QCs were measured against fresh calibrators, but that the calibrator had
to be frozen to get agreement, it would concern me that something was
changing in the sample when it was frozen. I would need to investigate
further to determine how it might affect quantification in study
samples, and whether matched frozen samples, QCs and calibrators, might
actually all be losing/gaining something on freezing.
-Tom
Thomas L. Tarnowski, Ph.D.
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