A method for preparing a pathogen inactivation treatment-ready blood product comprising: providing a container system 10 comprising at least a pre-connected interim container 12, a container 16 including a liquid synthetic medium, and a transfer container 14 wherein said medium container 16 and said transfer container 14 are in openable flow communication with said interim container 12 providing a source container 26 including a quantity of a blood component derived from an apheresis procedure, said source container 26 being separate from the container system 10 establishing fluid communication between said source container 26 and said interim container 12, transferring said apheresis-derived blood component to said interim container 12 centrifuging said interim container 12 to substantially separate said blood component into said blood component 64 and a supernatant component 62 substantially removing said supernatant component 62 from said interim container 12 and transferring the same to said empty transfer container 14 determining the amount of the supernatant component 62 remaining with said blood component 64 and combining a selected quantity of said blood component 64 with a selected quantity of said synthetic medium within said interim container 12 to provide a blood product with a pre-selected ratio of said supernatant component 62 to said synthetic medium effective for said pathogen inactivation treatment.
