Systems and methods are disclosed for detecting an interruption of connection between a blood treatment apparatus and a patient blood circulation. The system includes a line shut-off for blocking the venous fluid line arranged between the blood treatment apparatus and a connector, an arterial fluid line arranged between the blood treatment apparatus and the patient blood circulation, a pressure sensor arranged in the venous fluid line or the arterial fluid line for measuring pressure, and a control and evaluation unit for evaluating a pressure curve in time of the pressure measured by the pressure sensor during blocking of the venous fluid line to detect an interruption or disturbance of the connection between the first connection means and the patient blood circulation.
