Sanne de Bruin

178 Chapter 7 Summary Background: Labeling of platelets is required to measure the recovery and survival of transfused platelets in vivo . Currently a radioactive method is used to label platelets. However, application of those radio-labeling methods are limited by both safety issues and the inability to isolate transfused platelets from the circulation. Biotinlabeled plate- lets (bioPLT) are an attractive non-radioactive option. However, no validated protocol to biotinylate platelets is currently available for human studies. Study design and meth- ods: Six platelet concentrates (PCs) derived frompooled buffy coats were sub-aliquoted and biotinylated at day 1 and day 7 of storage. To distinguish the effect of the processing steps from the effects of biotin incubation, two control groups were used: 1) ‘sham’ samples were processed on day 1 and day 7 but without the biotinylation reagent and 2) control samples were assessed on day 1 and day 7 but without any processing other than the PC isolation. For the biotinylation procedure, 50 ml of PCs was washed twice and incubatedwith 5mg/L biotin for 30minutes in a closed system. Stability of the biotin label after irradiation and storage of the biotin-solution was quantified. As measure of platelet activation, phosphatidylserine exposure and CD62p expression were assessed. Results: The biotin labeling density was reproducible. After biotinylation, 98.4%± 0.9% of platelets were labeled. Platelet counts, pH and ‘swirling’ were within the range ac- cepted by the Dutch blood bank for standard platelet products. Biotinylated platelets were not more activated compared to sham samples, but were more activated than the controls. Conclusion: We developed a standardized and reproducible protocol according to Good Practice Guidelines (GPG) standards, for biotin-labeling of platelets for clinical purposes. This method can be applied as non-radioactive alternative assess survival and recovery of transfused platelets in vivo .