A method of monitoring a vascular access during extra-corporeal blood treatment in which blood flows from the vascular access via an arterial segment of an extra-corporeal blood circuit into a blood-treating element, and from the blood-treating element via a venous segment back into the vascular access, comprising the steps of:
- measuring the pressure in the venous and arterial segments of the extra-corporeal blood circuit;
- determining a test function that defines interference affecting the measured arterial and venous pressures;
- determining a pressure differential that is freed from interference from the measured venous and arterial pressures;
- and
- analyzing the pressure differential that has been freed from interference to detect a faulty vascular access.