Investigation: the samples were not returned for investigation and we therefore conducted the following investigations based on the information provided.In making the blood bags concerned, sealed bags are filled with solution and the line is assembled.These bags are sterilized, stacked, and placed into the blister packs.The top film of each blister pack is heat-sealed.In making leukoreduction filters, filter membranes are formed and put in filter housings.We reviewed the manufacturing record of the lot number in question.There was no equipment trouble causing the issue concerned and we confirmed that the equipment had operated properly and no anomalies had been observed.We also reviewed the manufacturing record regarding particulate removal rates of filter membranes that were likely to be related to filtration performance.It was confirmed that all filter membranes conformed to all standards.Release testing, which includes measurements of solution concentration and volume and a visual inspection, is performed on the product concerned on a sample basis.We reviewed each testing and inspection record of the production number and confirmed that there were no anomalies in all release testing items.The product conformed to the standards.We confirmed that we had not received complaints relating to the lot number in question from any other customers as of december 2, 2021.Root cause: from the above-mentioned investigation results, we did not observe any abnormalities in the manufacturing process of the lot number concerned.The filter membranes of the product concerned consist of a rough pore pre-membrane (the first filter membrane) and minute pore main-membranes (the second through eighth filter membranes).According to the data at the time of designing of the product in question, there is a possibility of white blood cell contamination when the particulate removal rates are low.However, as mentioned above, the particulate removal rates of the lot number concerned were within the standards and did not show a low tendency.Therefore, we were not able to identify the cause of the issue.
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