agregate of platelets

Hi every body

Last month quality control department in my blood bank  canceled  208 from 499 of PCs units which derived by PRP method and there are 30% of cancelled units due to aggregete platelets, by visually assessment the next day of preparation, so do you have any idea about possible causes of platelet aggregation.

Thank you

Edited January 16, 201510 yr by azizka71