The invention concerns a filtering unit for selectively eliminating a target substance from a biological fluid such as blood or a blood component, said unit comprising a filtering media (5) including, stacked from upstream to downstream: an upstream structure (6) for eliminating at least the target substance, said structure comprising a stack of layers (7) based on a nonwoven material having pores of diameter D, said structure further comprising, interposed between at least some of the layers (7) of the upstream structure, particles (8) of average diameter greater than diameter D, said particles (8) exhibiting an affinity for the target substance； a downstream structure (9) for retaining the particles (8) which consists of at least one layer (10) of porous material, the average diameter of the pores of said material being not greater than diameter D.
