Device (5) for filtering blood including a filter unit (7) having a blood filter, an inlet (8) for blood to be filtered and being connectable to an artery of a patient and a blood outlet (9) for filtered blood and being connectable to a vein of the patient, and having a filtrate container (6,14), that encloses the filter unit (7), for receiving filtrate (12) passing through the blood filter during a filtering process and that the filtrate container (6,14) is a closed container, which in a filled state is arranged to establish a counter-pressure over the blood filter, whereby the filtering process is interrupted. The invention also concerns a system including the above device.