The invention relates to systems and methods for sensing fluid characteristics of peritoneal dialysate infused into and removed from a patient during treatment. The systems and methods include sensors, processors, and flow paths for determining patient health based on the fluid characteristics of the peritoneal dialysate. The system can be a peritoneal dialysis cycler which can include an infusion line; an effluent line; at least one pump positioned in the infusion and/or effluent line; and at least one sensor fluidly connected to the effluent line. The sensor can be at least one of a flow sensor, an ion selective electrode, a pH sensor, a pressure sensor, a refractive index sensor, and a temperature sensor. The method can include infusing peritoneal dialysate through an infusion line; removing peritoneal dialysate through an effluent line; and determining at least one fluid characteristic of the peritoneal dialysate in the effluent line.