A device is described for interrogating human skin using tight coupling between the transmitter and receiver of the millimeter waves (MMWs). Methods are provided to evaluate changes in the amplitude and/or phase of the transmitted MMWs in order to estimate the blood concentration of glucose. Using this device and the related methods, the blood glucose concentration or a change in the blood glucose concentration can be monitored for diagnosing diabetes mellitus and other metabolic disorders of carbohydrate metabolism characterized by either high blood glucose level (hyperglycemia) or low blood glucose level (hypoglycemia), as well as for monitoring (including self-monitoring) a metabolic disorder progression or an efficacy of treatment.
