Back to the Top
I am concerned re the use of frozen curves and frozen QC to measure
accuracy and stability. For Example, we have Sponsors who insist on
doing this 1) as an apparent efficiency or, 2) because the use of fresh
does not work.
In answer to 1) its not an efficiency unless it is accurate and to 2)if
fresh does not work it may be necessay to characterize why and try to
fix the assay.
1. Do you compare fresh vs frozen curves and QC?
2. Do you run fresh curves and fresh QC for accuracy and precision ? if
not what is used?
3. Do you run stability freeze thaw, refrigerator, freezer, bench top)
samples using plates with fresh curves and fresh QCs? if not what do you
use to accept a run/plate?
4. Do you accept stability based on nominal or against the value
returned for the T0 stability samples? Do you use raw response as an
additional measure?
5. Do you freeze and use frozen curve points for sample analysis?
Ed O'Connor, PhD
Technical Director, Immunoanalytical
Tandem Laboratories
115 Silvia Street
West Trenton, New Jersey
609-228-0243
Back to the Top
Dear Ed,
Regarding the questions about fresh or frozen curves and QCs, I'm not
sure I can answer all your questions without knowing the details of
the method and the analyte. The most important thing to keep in mind
is that the data collected from QCs should represent what you can
expect from actual study samples. Therefore, if the samples you
intend to analyze are to be before analysis, frozen, then the QCs
should also be frozen. The precision and accuracy data for QCs
stored frozen will then represent what you should expect for the
corresponding samples. If your samples are never frozen, then it
would be best to collect precision and accuracy data from never-
frozen QCs; however in that case it might be useful to collect
precision and accuracy data from frozen QCs as well. If the
precision and accuracy for frozen QCs are equivalent to precision and
accuracy for fresh QCs, you can use frozen QCs instead of fresh ones
during a run to determine whether or not to accept the run.
It is more common to use freshly prepared calibration standards, but
if the QC samples stored under conditions equivalent to those used
for samples produce accurate results with a set of calibration
standards prepared and stored according to your choice, then there is
evidence/justification that the chosen preparation and storage of
calibration standards is OK.
Similarly, stability should be determined with QCs for conditions
expected to be experienced by the study samples. This is usually
determined in separate experiments for QCs frozen long term at a
specified freezer temperature, thawed but held refrigerated,
subjected to cycles of freeze and thaw, and possibly held at room
temperature; it all depends what the actual samples are expected to
experience.
Be sure to document what you decide to do and justify scientifically
why it is reasonable.
This is in answer to questions below regarding the use of fresh or
frozen calibration standards and QCs:
> I am concerned re the use of frozen curves and frozen QC to measure
> accuracy and stability. For Example, we have Sponsors who insist on
> doing this 1) as an apparent efficiency or, 2) because the use of
fresh
> does not work.
> In answer to 1) its not an efficiency unless it is accurate and to
2)if
> fresh does not work it may be necessay to characterize why and try to
> fix the assay.
> 1. Do you compare fresh vs frozen curves and QC?
> 2. Do you run fresh curves and fresh QC for accuracy and
precision ? if
> not what is used?
> 3. Do you run stability freeze thaw, refrigerator, freezer,
bench top)
> samples using plates with fresh curves and fresh QCs? if not what
do you
> use to accept a run/plate?
> 4. Do you accept stability based on nominal or against the value
> returned for the T0 stability samples? Do you use raw response as an
> additional measure?
> 5. Do you freeze and use frozen curve points for sample analysis?
Hope that this helps.
Tom Tarnowski
Thomas L. Tarnowski, Ph.D.
Bioanalytical Development, Elan Pharmaceuticals
Thomas.Tarnowski.-a-.elan.com
Back to the Top
The following message was posted to: PharmPK
Dear Ed,
If you use fresh, are the standard solutions you use to spike standards
and QC's stored, or do you prepare them also fresh?
Regards Bert
PharmPK Discussion List Archive Index page
Copyright 1995-2010 David W. A. Bourne (david@boomer.org)