Retention of clinical biosamples / blank matrices [Regulatives / Guidelines]
I am not aware of any retention period mentioned in any of the main BE guidelines. It is a matter of agreement between the sponsor and the CRO.
Usually CROs keep the samples until the study report is approved by the sponsor. This makes sense, of course. Some sponsors will ask the CRO to keep the samples until the application is approved. Most CROs will charge for storage beyond a few months.
In any case it makes little sense to store the samples beyond their demonstrated stability period. If they are stored for a longer duration: I would recommend to store QC samples along with them. If the samples need to be re-analysed, you can then demonstrate stability (or instability).