A medical instrument (300, 700, 1300, 1400, 1500, 1600) for performing a measurement (1513) on a biological sample using a test strip (310), wherein the medical instrument comprises: a housing (302) and an analytical unit (1508) for analyzing the test strip, wherein the analytical unit is within an interior volume (308). The analytical unit comprises a test strip mount (1510) configured for receiving the test strip to perform the measurement. The instrument further comprises a test strip port (312) between an exterior surface (304) and an interior surface (306). The test strip port is aligned with the test strip mount along an insertion direction (328). The medical instrument further comprises a shutter (100) for sealing the test port. The shutter is configured for being in a open position and a closed position. The shutter is within the interior volume. The shutter is configured for sealing the test port when in the closed position. The shutter comprises a test strip opening (106). The test strip opening is aligned with the test strip port and the test strip mount when the shutter is in the open position. The shutter has a first sealing surface (118). The test strip port has a second sealing surface (120). The first sealing surface and the second sealing surface are configured to mate in the closed position. The shutter comprises a mechanism for moving the shutter between the open position and the closed position. Moving the shutter between the closed position and the open position comprises a rotation of the shutter parallel to the insertion direction. The medical instrument further comprises an actuator (2506) for actuating the mechanism to move the shutter between the open position and the closed position.
