A dialysis system includes a dialysis fluid cassette-based membrane blood pump; a dialyzer in fluid communication with the blood pump: first and second dialysis fluid cassette-based balance chambers each having (i) a fresh dialysis fluid compartment in fluid communication with the dialyzer and (ii) a spent dialysis fluid compartment; a dialysis fluid cassette-based fresh dialysis fluid membrane pump in fluid communication with the fresh dialysis fluid compartments of the first and second balance chambers; a dialysis fluid cassette-based spent dialysis fluid membrane pump in fluid communication with the dialyzer and the spent dialysis fluid compartments of the first and second balance chambers; and arterial and venous lines in fluid communication with the dialyzer for patient connection, the arterial and venous lines each including a contact used for electrically detecting a patient access disconnection.