Greetings folks,
I have three months of turtle plasma samples in my freezer that unfortunately did not close properly and results in Some of the samples thawing. The freezer normally sits between -20-30c and most of it remained frozen but samples near the front thawed. They were still cold to the touch upon discovery. I'll be using this plasma for steroid hormone quantification in turtles (E2, P4 and T), I know steroids don't tend to break down as a quickly as some other compounds but just curious to see if folks think these samples should be ok to run via assay and give accurate results still.
Cheers,
Jordan
You probably have standard samples that you treated the same way as your unknown samples. I suggest that you simply assay a few of the standards after a freeze-thaw-refreeze cycle to see if they have kept their potency for each steroid after a similar cycle. This idea may not be quite so 'perfect' if the standards were not saved in turtle plasma. You might be able to make a preliminary assessment by looking at the protocol you have for storing and using the standards. But as I was taught a while ago an approximation is not as good as a test.
As far as I know, steroids tend to be stable if kept cold. Whether cool to the touch for a short time does any harm is doubtful, at least to me. Do you have duplicate aliquots that you could run together?
Hello!
It is important that samples are not exposed to thawing / re-freezing cycles.
You can analyze some of the doubtful samples to estimate their condition, as recomended. If your partly de-frozen samples from one experimental group, then using statistical methods (for example, Kolmogorov-Smirnov Test, Mann-Whitney, etc.), you will be able to understand the normal distribution of the results.
Jordan, your question actually only may be addressed by a stability test (spiked samples, freeze them and then store them at different temperatures for some time). Depending on the results of your analysis and the importance of the conclusions you are drawing from them, it might make sense to set up such a test in order to corroborate your results.
On the other hand, if the samples are sterile, I'd be quite confident that no adverse effects have been happening. Are the steroids sensitive to oxygen or modification by enzymes which are released by broken blood cells? Are you observing hemolysis?
If you know the positions of your samples in the fridge, esp. if you are able to identify those which have been thawed, you could plot the results against the sample position/thawing status to check if the thawed samples are producing weird data.
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