A peritoneal dialysis system includes a removable cassette defining a flexible pump chamber and a pressure sensing area that is fluidly connected to the pump chamber wherein, during operation of the peritoneal dialysis system, peritoneal dialysis fluid is contained in the pump chamber; and a peritoneal dialysis machine configured to secure the removable cassette, peritoneal dialysis machine including (i) a pressure sensor positioned to align with and to contact the pressure sensing area of the removable cassette when the removable cassette is secured to the peritoneal dialysis machine, and (ii) a controller connected to the pressure sensor and adapted to change the operation of the peritoneal dialysis machine in response to changes in pressure sensed by the pressure sensor, wherein the pressure sensor and the pressure sensing area are arranged so that the pressure sensor measures a pressure of fluid in a fluid passage between the pump chamber and a patient during operation of the peritoneal dialysis system.