A method of operating a medical instrument (2500, 2600), wherein the medical instrument is an analyzer for performing a measurement on a biological sample using a test strip, wherein the medical instrument comprises: - a housing with an exterior surface, wherein the housing comprises an internal surface surrounding a interior volume; - an analytical unit for analyzing the test strip, wherein the analytical unit is within the interior volume, wherein the analytical unit comprises a test strip mount configured for receiving the test strip to perform the measurement; - a test strip port between the exterior surface and the interior surface, wherein the test strip port is configured for receiving the test strip, wherein the test strip port is aligned with the test strip mount along an insertion direction; - a shutter for sealing the test strip port, wherein the shutter is configured for being in a open position and a closed position, wherein the shutter is within the interior volume, wherein the shutter is configured for sealing the test strip port when in the closed position, wherein the shutter comprises a test strip support, wherein the test strip support is aligned with the test strip port and the test strip mount when the shutter is in the open position, wherein the shutter has a first sealing surface, wherein the test strip port has a second sealing surface, wherein the first sealing surface and the second sealing surface are configured to mate in the closed position, wherein the shutter comprises a mechanism (100, 600, 1900, 2501, 2502) for moving the shutter between the open position and the closed position, wherein moving the shutter between the closed position and the open position comprises a rotation of the shutter perpendicular to the insertion direction; and - an actuator for actuating the mechanism to move the shutter between the open position and the closed position; wherein the method comprises the steps of: - controlling the actuator to actuate the mechanism to move the shutter in the open position; - placing the biological sample on the test strip; - inserting the test strip into the test strip port such that the test strip passes through the test strip support and into the test strip mount; - analyzing the test strip with the analytical unit to perform the measurement; - remove the test strip from the medical instrument; - controlling the actuator to actuate the mechanism to move the shutter in the closed position; and - clean the exterior surface of the medical instrument. - a housing with an exterior surface, wherein the housing comprises an internal surface surrounding a interior volume; - an analytical unit for analyzing the test strip, wherein the analytical unit is within the interior volume, wherein the analytical unit comprises a test strip mount configured for receiving the test strip to perform the measurement; - a test strip port between the exterior surface and the interior surface, wherein the test strip port is configured for receiving the test strip, wherein the test strip port is aligned with the test strip mount along an insertion direction; - a shutter for sealing the test strip port, wherein the shutter is configured for being in a open position and a closed position, wherein the shutter is within the interior volume, wherein the shutter is configured for sealing the test strip port when in the closed position, wherein the shutter comprises a test strip support, wherein the test strip support is aligned with the test strip port and the test strip mount when the shutter is in the open position, wherein the shutter has a first sealing surface, wherein the test strip port has a second sealing surface, wherein the first sealing surface and the second sealing surface are configured to mate in the closed position, wherein the shutter comprises a mechanism (100, 600, 1900, 2501, 2502) for moving the shutter between the open position and the closed position, wherein moving the shutter between the closed position and the open position comprises a rotation of the shutter perpendicular to the insertion direction; and - an actuator for actuating the mechanism to move the shutter between the open position and the closed position; - controlling the actuator to actuate the mechanism to move the shutter in the open position; - placing the biological sample on the test strip; - inserting the test strip into the test strip port such that the test strip passes through the test strip support and into the test strip mount; - analyzing the test strip with the analytical unit to perform the measurement; - remove the test strip from the medical instrument; - controlling the actuator to actuate the mechanism to move the shutter in the closed position; and - clean the exterior surface of the medical instrument.