A whole blood filtration device is provided with a filter membrane separating a feeding volume and a clean side of the filter membrane from each other. The feeding volume communicates with a first feeding side opening and with a second feeding side opening. The filter membrane has pores with a pore size that ensures permeability of the filter membrane to blood plasma/serum and that retains blood cells. The first feeding side opening can be coupled to a first blood pump for feeding blood from the first feeding side opening into the feeding volume so that blood plasma/serum permeates the filter membrane and blood cells, retained by the filter membrane, exit from the feeding volume through the second feeding side opening.