A rest period before agitation may improve some in vitro apheresis platelet parameters during storage

BACKGROUND: Whole blood-derived platelets (PLTs) prepared by the PLT-rich plasma method are subjected to a recommended 1-hour rest period after the second centrifugation to avoid excessive PLT activation. Different apheresis PLT preparation methods demonstrate different levels of PLT activation and ability to form macroscopic aggregates immediately after collection. PLT collections are lost on Day 1 of storage if aggregates are not dispersed. It is possible that a rest period may help to disperse PLT aggregates. It is not established whether apheresis PLTs require a rest period before agitation and what the length of this period should be. STUDY DESIGN AND METHODS: Apheresis PLTs (Amicus, Fenwal, Inc.) were divided into five identical aliquots. One aliquot was placed on the flatbed agitator immediately after division. The other aliquots were subjected to agitation after 1, 2, 4, and 6 hours of rest. Samples were taken on Days 1, 5, and 7 for standard PLT assays. RESULTS: No differences during 7-day storage were observed in PLT content, mean PLT volume, pH levels, bicarbonate, glucose, lactate, oxygen and carbon dioxide levels, hypotonic shock response, aggregation, and activation markers in PLT aliquots subjected to different rest periods or without a rest period. In contrast, values of extent of shape change, percentage of discoid PLTs, and expression of GP1b-a were greater in aliquots subjected to different periods of rest compared to those of PLTs without a rest period. CONCLUSION: A rest period from 1 to 6 hours may improve some but not all in vitro PLT storage parameters.