A medical filter (11) is constructed as a container with an interior volume in open fluid communication with a patient connection element (31) and a transport connection element (39). Filter support structure (13), mounted within the interior, is structured as a thin, perforated member (14) carrying hydrophilic filter medium (17). A first flow path directs spent dialysate from the patient across the surface of the filter medium (17) to the transport connection (39). A second flow path directs fresh dialysate from the transport connection (39) through the filter medium (17) and the perforated support structure (13) to the patient connection (31).