RELATIVE EFFICIENCY OF LEUKOCYTE REMOVAL PROCEDURES FOR THE PRODUCTION OF LEUKOCYTE-POOR RED-CELL CONCENTRATES ASSESSED BY FLOW-CYTOMETRY

Flow cytometry was used to: (1) determine residual leucocyte numbers i n red cell suspensions following the range of leucocyte depletion proc edures used in our organisation, and (2) to characterise phenotypicall y the leucocytes using direct immuofluorescence with monoclonal antibo dies to cell surface receptors. Under the conditions used, a lower lim it of detection of 2.5 leucocytes per mu l (equivalent to 3.43 log(10) or 99.96% removal) could be achieved. Filtration through polyester fi lters was found to remove up to > 99.96% of the initial leucocytes; ho wever, a significant differential efficacy was observed between filter s from different manufacturers even when filters with similar costs we re compared. The order of filter brands with respect to leucocyte remo val found was Pall BPF4 = Erypur Optima G-O > Sepacell R500 > Pall RC5 0. Phenotyping revealed that increasing filtration efficacy was associ ated with a preferential removal of lymphocytes; conversely, a second filtration over one brand of filter allowed proportionately more lymph ocytes to pass through compared with the first filtration. A saline wa sh following filtration removed a further 0.5% of the initial leucocyt e content, and was associated with a preferential loss of granulocytes . Freeze-thawing the red cell suspension removed fewer leucocytes (96. 3%) than did filtration (98.74% to > 99.6%) or filtration followed by washing (99.22%), and also led to preferential loss of granulocytes. F low cytometry provides a reliable tool for the quality control of leuc o-depleted red cells, and allows a qualitative assessment of the resid ual leucocytes. This information is of value in choosing procedures ai med at decreasing the risk of alloimmunisation and post-transfusion re actions.