Plasma could be helpful for your test.

Hi Joseph, I had similar concerns when working with aptamer derived data sets for serum (no plasma was available in that study). We performed correlations with circulating platelets (as well as leucocytes as leucocyte activation might be triggered during clot activation). Much to my surprise we did not observe any correlation. So might consider a similar approach if you have blood count data available.

Hi Joseph, Do you mean the platelet-rich plasma (PRP) is frozen? If this is the case, you also have platelet degranulation here. Platelets are very sensitive, changing temperature, freezing/thawing will activate platelets. You can confirm this by flow cytometry (CD62P/PAC1). Some labs actually use freezing/thawing as a non-pharmacological way to prepare platelet releasate. I am afraid both serum and plasma will have contamination from platelets granules. In our lab, if we looking at a growth factor that is also present in platelets, we will isolate platelets first (in a very gentle way), then freeze the plasma. Also, platelet count does not reflect degranulation. If you can not get fresh samples, and you have to do this, I will use the plasma, keeping in mind the results will need confirmation using fresh samples.

Thanks all for the responses. No easy answer it seems! I've ordered another set of tests to be run on plasmas that were collected at the same time as the serum to see if there is any difference.

@Jan - will look at the platelet count as you suggested. This is probably relevant to the pathology I'm interested in too!