I intend to open this thread with an unconventional inquiry. 

As part of a hypothesis to check for metabolic changes in patients treated with antipsychotics, we drew blood in EDTA tubes 5-19 years ago, centrifuged the samples immediately, withdrew the serum and froze it (-80°C) with dry ice. The samples were frozen out once for the purpose of creating aliquots and refrozen immediately. There was no proteinase inhibitor added. 

We were wondering whether we can use these samples to detect neuropeptides such as NPY, AGRP, alpha MSH or other molecules (yet to be specified) as Insulin for example with ELISA. Also, is there a maximum time span that you can store samples as such? We would be keen to know that too, so in case 19 years is too long we would use the ones that are less "old" and create a "sub-cohort".

Looking forward to hearing from you