Abstract: The present invention relates to an apparatus (1) for holding a disposable medical item, in particular a dialyzer (2), plasma filter or adsorbent, for treating blood, a system (10) comprising such an apparatus, and a method for operating a disposable medical item for treating blood. A bearing device (4) is thereby configured to rotatably support the disposable item, and a drive device (5) is thereby configured to rotate the rotatably mounted disposable item around a longitudinal axis (L) extending substantially in a direction in which the blood flows through the disposable item when the disposable item is in operation. Alternatively or additionally, a sensor device (6) is configured to detect a rotation of the rotatably mounted disposable item around at least one rotational axis (L, Q), in particular around the longitudinal axis (L) and/or around a transverse axis (Q) running perpendicular to the longitudinal axis (L) and output corresponding sensor data.