APPARATUS AND METHOD

Haemodialysis machine 1 comprises an extracorporeal blood circuit 10, a dialyser 20, a dialysate circuit 30 and a control unit 40. The dialyser 20 is in fluid communication with the extracorporeal blood circuit (EC) 10 and dialysate circuit 30. An extracorporeal blood sensor unit 50 comprises an analyte sensor 51 and an auxiliary circuit 52. The sensor unit has a first arrangement where the analyte sensor 51 is in fluid communication with the extracorporeal blood circuit 10 via a divert 11 branching from the circuit. The sensor unit has a second arrangement where the analyte sensor 51 is in fluid communication with the auxiliary circuit 52. A valve 522 in the sensor unit 50 controls fluid communication. Embodiments allow for fluid communication between the sensor unit 50 and dialysate circuit 30, or sensor unit and other parts of the blood circuit. Sensor unit 50 determines blood analyte levels or dialysate levels to provide real-time determination of patient specific needs during haemodialysis treatment. The auxiliary circuit 52 can be used to flush and clean the sensor 51.