This report is being filed to provide additional information in h.6 and h.10.Investigation: the sets concerned were not returned for evaluation.We therefore conducted investigations based on the provided information.In regard to the production of imuflex, 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.For the leukoreduction filter, filter membranes are punched out, laminated, and integrated into soft housing.In order to ensure leukoreduction performance and to prevent filter occlusion in and hemolysis, standards have been set to control particulate removal rates and cationization levels of each filter membrane.The standards of average cationization levels of laminated filter membranes have also been set and controlled.We reviewed the manufacturing record of the lot number in question and confirmed that no anomalies occurred in any process, and the products were manufactured as usual.In addition, we investigated dope material used for the lot number in question and found that the viscosity of pu solution of dope material conformed to the 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.Regarding the retained sample of the lot number concerned, three sets were visually inspected.There were no abnormalities in their appearances.We used one of the sets to measure the solution volume and used another one of the sets to perform a quantitative test for the composition of the solution in the same manner as the release testing.The measured results conformed to our in-house standards.Root cause: we reviewed the manufacturing record and the testing and inspection record of the lot number concerned; however, we did not find any abnormalities and we were not able to identify the cause of the issue.Wbc contamination is commonly caused by the following factors: blood characteristics of donors there is a possibility of wbc contamination due to blood characteristics of donors.2) pressure loaded on filter membranes for some reason, where a physical stress on filter membranes is greater than what is expected, trapped white blood cells are pushed out of the filter membranes and may result in wbc contamination.For the prevention of wbc contamination, the instructions for use (ifu) of the product state: "[caution] do not squeeze or apply pressure on the filter while it is attached to the bag containing the filtered blood", and ¿clamp the blood filled tubing before blood enters the filter¿.We confirmed in some complaints previously reported that the following cases caused wbc contamination.- blood was filtered within 30 minutes after blood collection.- the tube below the filter was not clamped before blood flowed into the filter when expelling air.
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