A renal failure blood therapy system includes: (i) a renal failure blood therapy machine; (ii) a therapy prescription for a patient treated by the renal failure blood therapy machine to remove a solute from the patient's blood; (iii) a test including multiple blood samples taken at multiple times during a test therapy to determine concentration levels of the solute at each of the multiple times; and (iv) a device programmed to use a kinetic model for the solute in a first instance with at least one of the concentration levels of the solute to estimate at least one estimated patient parameter. The device is further programmed to enable a user to determine at least one of a therapy duration, a therapy frequency, a dialysate flowrate or a blood flowrate for the therapy prescription.