Abstract: A real-time, non-invasive system and method for determining the level of an analyte of interest in the urine of a patient is disclosed. The system and method uses the measured level of an analyte of interest to detect the onset of acute renal failure (ARF) as early as possible to prevent that patient from developing the disease or mitigating the effects of the disease. The system and method may be used to monitor the recovery of a patient after an ARF diagnosis. Preferably, the analyte of interest is creatinine or urea. The system may be placed in the urine drain line of a patient between a Foley catheter or other urinary drain and a urine collection bag.