Patent ID: 8496833

Claim:
A leukocyte removal method comprising filtering blood containing leukocytes using a leukocyte removal filter including plural fibrous filter materials having different average fiber diameters to remove the leukocytes in the blood, in which the fibrous filter materials include at least a leukocyte removal filter material A having an average fiber diameter of not less than 2.1 μm to less than 4.0 μm and a leukocyte removal filter material B having an average fiber diameter of not less than 0.7 μm to less than 1.2 μm, the filter material B is disposed downstream of the filter material A, and the average fiber diameter of the leukocyte removal filter material B is more than 17.5% to less than 50% of the average fiber diameter of the filter material A, wherein the leukocyte removal filter has a geometric mean (X×Y) 0.5 of X and Y of not less than 0.5 to not more than 1 when a ratio (t a /t c ) of a filtration time at a temperature of 20 to 24° C. (t a ) to a filtration time at a temperature of 1 to 6° C. (t c ) is assumed to be X, and a ratio (r a /r c ) of a leukocyte removal filtration performance in the temperature of 20 to 24° C. (r a ) to a leukocyte removal filtration performance in the temperature of 1 to 6° C. (r c ) is assumed to be Y.