A light shield (10, 22, 32, 44, 46a, 46b) is arranged in a light shielding position with respect to a sensor or a blood leakage detector installed in a medical apparatus and monitoring for changes of transmittance in a translucent fluid carried in a tubing (14, 42) connected to the medical apparatus. The light shield (10, 22, 32, 44, 46a, 46b) has a non-transparent configuration and is configured to prevent environmental light from being incident on a relevant detection active sensor area. Further, a disposable kit for a medical apparatus which is arranged to be mounted to the medical apparatus and to carry pre-installed disposables to be used during a medical treatment comprises a hard-shell subassembly (20) arranged to be positioned in a region of the medical apparatus in the vicinity of a detection active sensor area of a sensor which is sensitive to light and installed in the medical apparatus. At least one light shield element is selected from first to third light shield elements (10, 22, 32), and the at least one light shield element is mounted to the hard-shell subassembly (20) of the disposable kit in a region where the detection active sensor area is underneath.
