Investigation: one set of blood bags with the filter from the collection set was returned forevaluation.The leukoreduction filter was tested for flow rate and air leaks.A swift flow rate of 40ml/min was noted, and it was confirmed there were no air leaks.The filter was disassembled to observe the appearance of filter membranes and noticed creasesin the filter membranes of the filter.The creases in the filter were not different from those inconforming products and no aggregation was observed in any filter membranes.The manufacturing records, test records, and inspection records were reviewed forabnormalities and none were found.The records regarding the particulate removal rates of the filter membranes were reviewed.Allmembranes conformed to established specification.Shipping testing was performed on the reserve samples from the reported lot number.Thereserve samples were also visually examined, and the solution volume and solution compositionwere tested with no abnormalities noted.All product conformed to the establishedspecification.Root cause: based on the available information, it cannot be ruled out that the higher-than-expected wbc content in the whole blood product could be due to an occlusion, we noticedthat the first and fourth filter membranes from the inflow side of the filter were locally dyeddark with toluidine blue.The investigation showed no aggregation on any of the filtermembranes.Therefore, occlusion may have occurred, and blood may have been filtered by thefilter area which was smaller than usual and the linear speed (flow rate per unit area) increased,and then leukocyte leakage occurred.As an increase of wbc contamination complaints werenoted from previous lot numbers, further investigation was performed.Investigation resultsindicated that the cause of higher-than-expected wbc content in the whole blood productwas due to the maximum pore size of the filter membrane is likely to increase according to thecombination of multiple parameters in manufacture of leukoreduction filter membranes andwbc contamination is likely to occur frequently in the product lots of which the maximum poresize of the filter membrane has increased.The instructions for use provide a caution to notsqueeze or apply pressure to the filter while it is attached to the bag containing the filteredblood and also to clamp the blood-filled tubing before blood enters the filter in order to avoidleukocyte leakage.Corrective action: an internal capa has been initiated to review the maximum pore size ofthe filter membrane and the likelihood of an increase according to the combination of themultiple parameters.In addition, the wbc contamination is likely to occur frequently in theproduct lots of which the maximum pore size of the filter membrane has increased.To achievea resolution, manufacturing specifications were updated to narrow the range of the parametersin the manufacture of filter membranes and it was confirmed that the appropriate level of themaximum pore size of the filter membrane was achieved.
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