Leukoreduction of platelet concentrates using a 'polishing' filter

Filters for removal of leukocytes from platelet concentrates (PCs) usually have a large volume to guarantee sufficient leukoreduction. In this study, a small filter, with a volume of only 8 ml and therefore minimal platelet loss, for leukoreduction of PCs was investigated. This filter has a 'limited' leukoreducing capacity, hence the filter is called a 'polishing' filter.

PCs were made from 5 pooled buffy coats in either plasma or additive solution (PAS-II). After centrifugation, the platelet-rich supernatant was expressed on an automated separator (Compomat G4) to an empty transfer bag. The content of this transfer bag was filtered into the platelet storage bag, either by expression by lowering the top press of the Compomat G4, or by gravity by hanging it on a filtration rack.

Leukocyte counts before and after filtration revealed a mean leukoreducing capacity for the filter of 2.67 log(10) and a platelet loss of only 2% for PCs in PAS-II (n = 50), and for PCs in plasma a 3.43 log(10) leukoreduction with 3% platelet loss (n = 30). Expression of the PCs both in plasma and PAS-II through the filter using the Compomat G4 resulted in 10/10 units containing <5x10(6) leukocytes, but 1/10 PCs contained >1x10(6) leukocytes for both solutions. Filtration by gravity resultet in 40/40 units with <1x10(6) leukocytes for PCs in plasma, and 60/60 units with <1x10(6) for PCs in PAS-II.

The 'polishing' filter allows reliable, standardized and automated production of PCs, both in plasma and additive solution with minimal platelet loss, and containing uniformly <1x10(6) leukocytes, provided the filtration procedure is performed by gravity.