A biological fluid treatment device (1000) comprising: (a) a receptacle (600) comprising an inlet portion (100) that includes one or more holes (101a), an outlet portion (200) that includes a outlet port (201a) and a levigation fluid inlet port (300), and defining a fluid flow path between a hole (101a) of the inlet portion and the outlet port (201a) of the portion outlet and a fluid flow path between the inlet port (300) of levigation fluid of the outlet portion and a hole (101a) of the inlet portion； (b) a porous fibrous leukocyte extraction filter (500) having a first surface (501) and a second surface (502), disposed in the receptacle (600) through the fluid flow paths； and (c) a first perforated diffusion plate (400) having a first surface (410) and a second surface (420), the first surface (410) having a generally flat appearance, and the second surface (420) having a generally convex aspect, so that there is a gradual reduction in thickness from the center to the periphery of the first perforated diffusion plate (400), arranged in the receptacle (600) through the fluid flow paths, in which The first perforated diffusion plate (400) is disposed in the receptacle (600) between the second surface (502) of the leukocyte extraction filter (500) and the holes (201a, 300) of the outlet portion and the second surface (502) faces the exit hole (201a) of the exit portion.Un dispositivo de tratamiento de fluidos biológicos (1000) que comprende: (a) un receptáculo (600) que comprende una porción de entrada (100) que incluye uno o más orificios (101a), una porción de salida (200) que incluye un orificio de salida (201a) y un orificio de entrada de fluido de levigación (300), y que define una vía de flujo de fluido entre un orificio (101a) de la porción de entrada y el orificio de salida (201a) de la porción de salida y una vía de flujo de fluido entre el orificio (300) de entrada de fluido de levigación de la porción de salida y un orificio (101a) de la porción de entrada
