An example peritoneal dialysis system is disclosed. The example peritoneal dialysis system includes an automated peritoneal dialysis (“APD”) machine configured to remove ultrafiltrate (“UF”) from a patient and record how much UF has been removed. The APD machine operates according to a prescription to remove the UF. The system also includes a server in communication with the APD machine. The server analyzes the UF data to determine if the prescription is to be modified to compensate for changes to the patient's renal function or renal transport characteristics.