A method for detecting leakages in a system conducting a medical fluid, upstream a shut-off device of the system - wherein the system comprises a section conducting the medical fluid, the section being arranged upstream the shut-off device; - wherein the shut-off device is provided or intended for interrupting or reducing an outflow or escaping of the fluid out of the section into an area downstream the shut-off device; - wherein the system further comprises at least one conveying device for conveying the fluid through the section; wherein the method encompasses the steps of: - interrupting or reducing the fluid flow through the section or out of the section during a first conveying effort of the conveying device by means of setting or adjusting, respectively, the shut-off device for reaching a first conveying state in the section; - reaching a second conveying state in the section by changing the first conveying effort to a second conveying effort of the conveying device; characterized in that the method comprises the following further steps: - emitting at least one signal by means of a signal emitting device into the section of the system both in the first and the second conveying state; - receiving a proportion of the emitted signal leaving the section by means of a signal receiving device in the first conveying state as a first proportion; - receiving a proportion of the emitted signal leaving the section by means of a signal receiving device in the second conveying state as a second proportion; and - drawing a conclusion whether a leakage is present by means of an evaluation of the first proportion in relation to the second proportion, wherein drawing the conclusion is or encompasses an evaluation of the first proportion in relation to the second proportion and/or an evaluation of the calculated difference between the first and the second proportion in relation to a threshold value. - wherein the system comprises a section conducting the medical fluid, the section being arranged upstream the shut-off device; - wherein the shut-off device is provided or intended for interrupting or reducing an outflow or escaping of the fluid out of the section into an area downstream the shut-off device; - wherein the system further comprises at least one conveying device for conveying the fluid through the section; - interrupting or reducing the fluid flow through the section or out of the section during a first conveying effort of the conveying device by means of setting or adjusting, respectively, the shut-off device for reaching a first conveying state in the section; - reaching a second conveying state in the section by changing the first conveying effort to a second conveying effort of the conveying device; - emitting at least one signal by means of a signal emitting device into the section of the system both in the first and the second conveying state; - receiving a proportion of the emitted signal leaving the section by means of a signal receiving device in the first conveying state as a first proportion; - receiving a proportion of the emitted signal leaving the section by means of a signal receiving device in the second conveying state as a second proportion; and - drawing a conclusion whether a leakage is present by means of an evaluation of the first proportion in relation to the second proportion, wherein drawing the conclusion is or encompasses an evaluation of the first proportion in relation to the second proportion and/or an evaluation of the calculated difference between the first and the second proportion in relation to a threshold value.