White cell subsets in filtered red blood cell concentrates

• Leucoflex LCR 4 T/B-System gives a strong B lymphocyte reduction of 4.5 log10 in RCCs. • In filtered RCCs residual monocytes (48900/ RCC), T lymphocytes (16100/RCC) and B lymphocytes (6970/RCC) are at the lower detection limit of the procedure. • According to our knowledge, these data show for the first time that FACS-analysis of filtered RCCs is possible without previous WBC enrichment. • Contrary to other studies, we demonstrate a high content of residual granulocytes (90% of WBC) in leucodepleted RCCs. In the former studies, WBC enrichment by density gradient centrifugation before FACS-analysis results in loss of granulocytes and shift of WBC subsets by preparation [5,6]. • Since the granulocytes represent the major part of residual leucocytes and considering their low stability (half life 6 h), it is necessary to set the timepoint for WBC counting as quality control directly after preparation of filtered RCCs. • We recommend leucocyte immunphenotyping by FACS-analysis for evaluation of blood bag and filter systems and quality assurance of blood components in special cases.