An access disconnection system is described. The system comprises: an extracorporeal circuit arterial and venous contacts (163b, 163a) provided in the extracorporeal circuit arterial and venous patient access apparatuses a signal source (160) communicating with at least one of the arterial and venous contacts and configured to generate a signal within fluid flowing through the extracorporeal circuit and a sensing apparatus (168) configured to sense a first portion of the signal indicative of a first impedance produced by fluid flowing through the extracorporeal circuit. At least one of the arterial and venous contacts is placed close enough to a respective arterial and venous patient access apparatus such that a second portion of the signal indicative of a second impedance produced by fluid flowing through a parallel ground loop can be ignored.
